build(deps): bump actions/cache from 3 to 6

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 6.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](https://github.com/actions/cache/compare/v3...v6)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build.yml

@@ -186,7 +186,7 @@ jobs:
       if: matrix.build-arch == 'arm'
 
     - name: Download cached sysroot
-      uses: actions/cache@v3
+      uses: actions/cache@v6
       id: dl-cached-sysroot
       if: matrix.build-arch == 'arm'
       with: