ci: bump actions/cache in the actions group across 1 directory

Bumps the actions group with 1 update in the / directory: [actions/cache](https://github.com/actions/cache).


Updates `actions/cache` from 5.0.5 to 6.0.0
- [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/27d5ce7f107fe9357f9df03efb73ab90386fccae...2c8a9bd7457de244a408f35966fab2fb45fda9c8)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: actions
...

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

.github/workflows/diffuse.yml

@@ -47,7 +47,7 @@ jobs:
 
     - name: Cache base apk
       id: cache-base
-      uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5
+      uses: actions/cache@2c8a9bd7457de244a408f35966fab2fb45fda9c8 # v6.0.0
       # gh api repos/actions/cache/commits/v5 --jq '.sha'
       with:
         path: diffuse-base.apk