UID2-6913: Pin third-party GitHub Action refs to commit SHAs (#30)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: jon8787

.github/workflows/dev-docker-image.yml

@@ -9,6 +9,6 @@ jobs:
     - uses: actions/checkout@v3
 
     - name: Build development docker image
-      uses: docker/build-push-action@v4
+      uses: docker/build-push-action@0a97817b6ade9f46837855d676c4cca3a2471fc9 # v4
       with:
         push: false