ci: bump actions/cache from 4 to 5 (#65)

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Author: dependabot[bot]

.github/workflows/tests.yml

@@ -21,7 +21,7 @@ jobs:
         uses: Homebrew/actions/setup-homebrew@master
 
       - name: Cache Homebrew Bundler RubyGems
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ${{ steps.set-up-homebrew.outputs.gems-path }}
           key: ${{ matrix.os }}-rubygems-${{ steps.set-up-homebrew.outputs.gems-hash }}