DX-516: Pin actions to SHA

Author: scraswell

.github/workflows/main.yml

@@ -12,7 +12,7 @@ jobs:
       BUNDLE_PATH: ${{ github.workspace }}/vendor/bundle
     steps:
     - uses: actions/checkout@v2
-    - uses: ruby/setup-ruby@v1
+    - uses: ruby/setup-ruby@354a1ad156761f5ee2b7b13fa8e09943a5e8d252 # v1.229.0
       with:
         ruby-version: ${{ matrix.ruby }}
         bundler-cache: true