Update tests.yml cache v3->v4

Author: cboulay

.github/workflows/tests.yml

@@ -17,7 +17,7 @@ jobs:
 
       - name: Cache Homebrew Bundler RubyGems
         id: cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: ${{ steps.set-up-homebrew.outputs.gems-path }}
           key: ${{ runner.os }}-rubygems-${{ steps.set-up-homebrew.outputs.gems-hash }}