CI: Bump actions/cache from 4 to 5

Bumps [actions/cache](https://github.com/actions/cache) from 4 to 5.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v4...v5)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/macvim-buildtest.yaml

@@ -125,7 +125,7 @@ jobs:
       # Note: Legacy self-hosted runner already has this installed and doesn't need this.
       - name: Cache Python 2
         if: inputs.publish && !inputs.legacy
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: python27-cache
           key: ${{ inputs.os }}-python27