Bump julia-actions/cache from 2.0.1 to 2.0.4 (#772)

Bumps [julia-actions/cache](https://github.com/julia-actions/cache) from 2.0.1 to 2.0.4.
- [Release notes](https://github.com/julia-actions/cache/releases)
- [Changelog](https://github.com/julia-actions/cache/blob/main/devdocs/making_a_new_release.md)
- [Commits](julia-actions/cache@580d2b6...8608484)

---
updated-dependencies:
- dependency-name: julia-actions/cache
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/exercise-tests.yml

@@ -35,7 +35,7 @@ jobs:
         with:
           version: ${{ matrix.julia-version }}
 
-      - uses: julia-actions/cache@580d2b69d895343992af2cbad49c32a0149c2cde
+      - uses: julia-actions/cache@8608484607cba0bdb5437a7bad85d6502499d029
 
       - name: Install test dependencies
         run: julia --color=yes --project -e "using Pkg; Pkg.instantiate()"