ci: fix ruby/setup-ruby cache poisoning and stale version comment (#96)

- Disable bundler-cache and add explicit bundle install step to
  eliminate a zizmor cache-poisoning finding (bundler cache combined
  with docker/build-push-action publishing runtime artifacts)
- Correct the trailing version comment on ruby/setup-ruby from
  v1.310.0 to v1.315.0 to match the pinned commit SHA

Author: chorrell

.github/workflows/ruby.yml

@@ -20,10 +20,12 @@ jobs:
       with:
         persist-credentials: false
     - name: Set up Ruby ${{ matrix.ruby-version }}
-      uses: ruby/setup-ruby@0dafeac902942906541bc140009cdbf32665b601 # v1.310.0 # zizmor: ignore[cache-poisoning]
+      uses: ruby/setup-ruby@0dafeac902942906541bc140009cdbf32665b601 # v1.315.0
       with:
         ruby-version: ${{ matrix.ruby-version }}
-        bundler-cache: true
+        bundler-cache: false
+    - name: Install gems
+      run: bundle install
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@bb05f3f5519dd87d3ba754cc423b652a5edd6d2c # v4.2.0
       with: