Pin GHA to hash

Author: mhucka

.github/workflows/ci_docker_tests.yaml

@@ -66,7 +66,7 @@ jobs:
           submodules: recursive
 
       - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
+        uses: docker/setup-buildx-action@e468171a9de216ec08956ac3ada2f0791b6bd435 # v3
         with:
           driver: docker