Bump @actions/cache to v6.1.0 - handle read-only cache access

[jasongin]

Description

• Bump @actions/cache to v6.1.0 to pick up actions/toolkit#2435 Handle cache write error due to read-only token
• Switch redundant "Cache save failed" warning to debug log in save-only
• Add a section in README.md about read-only cache access
• Update generated JavaScript files under dist
• Update license files for dependencies
• Bump minor version in package.json from 6.0.0 to 6.1.0

Motivation and Context

The Actions service will soon issue tokens with read-only cache access to certain lower-trust worfklows such as pull_request_target. (Until now, read-write cache access was always granted.) Without this fix, the cache actions do not propagate errors from the service when attempting to write to the cache, resulting in a misleading warning message emitted to the workflow log: "Unable to reserve cache with key ${key}, another job may be creating this cache." After this change, the correct "cache write denied" warning will be emitted instead when that happens.

How Has This Been Tested?

• The @actions/cache change in the toolkit repo included updated unit tests.
• I ran end-to-end workflows with read-only cache tokens along with the changes in this PR and observed the resulting warnings emitted to the workflow log.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (add or update README or docs)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[Copilot]

Pull request overview

Updates this action to @actions/cache@5.1.0 to correctly surface “cache write denied” behavior when the workflow token has read-only cache permissions, reduces redundant warning noise in the save-only variant, and documents the new behavior.

Changes:

• Bump @actions/cache dependency and action version to 5.1.0
• Change save-only behavior to log a debug message (instead of an extra warning) when the cache is not saved
• Document read-only cache access behavior in the README and update release notes / license metadata

Show a summary per file

File	Description
src/saveImpl.ts	Avoids emitting a generic warning in save-only when saveCache returns -1; uses core.debug instead.
__tests__/saveOnly.test.ts	Updates expectations to assert debug logging and no warning / failure when save resolves to -1.
README.md	Adds a “Read-only access” section explaining restore-vs-save behavior with read-only tokens.
RELEASES.md	Adds a 5.1.0 changelog entry and minor markdown formatting cleanup.
package.json	Bumps package version to 5.1.0 and updates @actions/cache to ^5.1.0.
package-lock.json	Updates locked @actions/cache and transitive deps (but currently leaves the root package version at 5.0.4).
.licenses/npm/@actions/cache.dep.yml	Updates tracked license metadata for @actions/cache@5.1.0.
.licenses/npm/@azure/core-client.dep.yml	Updates tracked license metadata for @azure/core-client@1.10.2.
.licenses/npm/@azure/core-http-compat.dep.yml	Updates tracked license metadata for @azure/core-http-compat@2.4.0.
.licenses/npm/@azure/core-rest-pipeline.dep.yml	Updates tracked license metadata for @azure/core-rest-pipeline@1.24.0.
.licenses/npm/@azure/core-xml.dep.yml	Updates tracked license metadata for @azure/core-xml@1.5.1.
.licenses/npm/@azure/storage-blob.dep.yml	Updates tracked license metadata for @azure/storage-blob@12.32.0.
.licenses/npm/@azure/storage-common.dep.yml	Updates tracked license metadata for @azure/storage-common@12.4.0.
.licenses/npm/@typespec/ts-http-runtime.dep.yml	Updates tracked license metadata for @typespec/ts-http-runtime@0.3.6.
.licenses/npm/fast-xml-builder.dep.yml	Updates tracked license metadata for fast-xml-builder@1.2.0.
.licenses/npm/fast-xml-parser.dep.yml	Updates tracked license metadata for fast-xml-parser@5.9.2.
.licenses/npm/is-unsafe.dep.yml	Adds tracked license metadata for new transitive dep is-unsafe@1.0.1.
.licenses/npm/path-expression-matcher.dep.yml	Updates tracked license metadata for path-expression-matcher@1.5.0.
.licenses/npm/strnum.dep.yml	Updates tracked license metadata for strnum@2.4.1.
.licenses/npm/anynum.dep.yml	Adds tracked license metadata for new transitive dep anynum@1.0.1.
.licenses/npm/@nodable/entities.dep.yml	Adds tracked license metadata for new transitive dep @nodable/entities@2.2.0.
.licenses/npm/xml-naming.dep.yml	Adds tracked license metadata for new transitive dep xml-naming@0.1.0.

Copilot's findings

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• Files reviewed: 21/26 changed files
• Comments generated: 0

[jasongin]

I rebased to resolve conflicts from #1760

Since that change bumped the version to v6.0, this change now goes to v6.1.

[danwkennedy]

LGTM!