build(deps): bump actions/cache from 3 to 4

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v3...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/depexts.yml

@@ -190,7 +190,7 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v4
     - name: opam binary cache
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: binary/opam
         key: binary-${{ env.OPAMVERSION }}