build(deps): bump actions/cache from 5 to 6

Bumps [actions/cache](https://github.com/actions/cache) from 5 to 6.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v5...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>

Author: dependabot[bot]

.github/workflows/coverity.yml

@@ -99,7 +99,7 @@ jobs:
       # A cache miss will add ~30s to create, but a cache hit will save minutes.
       - name: restore the Coverity Build Tool
         id: cache
-        uses: actions/cache/restore@v5
+        uses: actions/cache/restore@v6
         with:
           path: ${{ runner.temp }}/cov-analysis
           key: cov-build-${{ env.COVERITY_LANGUAGE }}-${{ env.COVERITY_PLATFORM }}-${{ steps.lookup.outputs.hash }}
@@ -142,7 +142,7 @@ jobs:
           esac
       - name: cache the Coverity Build Tool
         if: steps.cache.outputs.cache-hit != 'true'
-        uses: actions/cache/save@v5
+        uses: actions/cache/save@v6
         with:
           path: ${{ runner.temp }}/cov-analysis
           key: cov-build-${{ env.COVERITY_LANGUAGE }}-${{ env.COVERITY_PLATFORM }}-${{ steps.lookup.outputs.hash }}