chore: pin GitHub Actions to SHAs [skip deploy]

Pins the following actions to their latest safe release (>5 days old):
- actions/checkout: pinned to v6.0.2 (de0fac2e)
- ruby/setup-ruby: pinned to v1.305.0 (0cb964fd)

Author: scottybarr

.github/workflows/default.yml

@@ -25,7 +25,7 @@ jobs:
         with:
           fetch-depth: 0
 
-      - uses: ruby/setup-ruby@v1
+      - uses: ruby/setup-ruby@0cb964fd540e0a24c900370abf38a33466142735 # v1.305.0
         with:
           bundler-cache: true
         env: