chore(deps): bump actions/cache from 4 to 6 (#10593)

Bumps [actions/cache](https://github.com/actions/cache) from 4 to 6.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v4...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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/backend_build_darwin.yml

@@ -82,7 +82,7 @@ jobs:
       # as the Linux registry cache.
       - name: Restore Homebrew cache
         id: brew-cache
-        uses: actions/cache/restore@v4
+        uses: actions/cache/restore@v6
         with:
           path: |
             ~/Library/Caches/Homebrew/downloads
@@ -142,7 +142,7 @@ jobs:
 
       - name: Save Homebrew cache
         if: github.event_name != 'pull_request' && steps.brew-cache.outputs.cache-hit != 'true'
-        uses: actions/cache/save@v4
+        uses: actions/cache/save@v6
         with:
           path: |
             ~/Library/Caches/Homebrew/downloads
@@ -178,7 +178,7 @@ jobs:
       - name: Restore ccache
         if: inputs.backend == 'llama-cpp'
         id: ccache-cache
-        uses: actions/cache/restore@v4
+        uses: actions/cache/restore@v6
         with:
           path: ~/Library/Caches/ccache
           key: ccache-llama-${{ runner.arch }}-${{ steps.llama-version.outputs.version }}-${{ github.run_id }}
@@ -211,7 +211,7 @@ jobs:
       - name: Restore Python wheel cache
         if: inputs.lang == 'python'
         id: pyenv-cache
-        uses: actions/cache/restore@v4
+        uses: actions/cache/restore@v6
         with:
           path: |
             ~/Library/Caches/pip
@@ -256,14 +256,14 @@ jobs:
 
       - name: Save ccache
         if: inputs.backend == 'llama-cpp' && github.event_name != 'pull_request'
-        uses: actions/cache/save@v4
+        uses: actions/cache/save@v6
         with:
           path: ~/Library/Caches/ccache
           key: ccache-llama-${{ runner.arch }}-${{ steps.llama-version.outputs.version }}-${{ github.run_id }}
 
       - name: Save Python wheel cache
         if: inputs.lang == 'python' && github.event_name != 'pull_request' && steps.pyenv-cache.outputs.cache-hit != 'true'
-        uses: actions/cache/save@v4
+        uses: actions/cache/save@v6
         with:
           path: |
             ~/Library/Caches/pip