fix: explicitly check if environment variable is true

.github/workflows/docker.yml

@@ -19,7 +19,7 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Log into the Docker container registry
-        if: ${{ env.SHOULD_PUSH_IMAGE }}
+        if: ${{ env.SHOULD_PUSH_IMAGE == 'true' }}
         uses: docker/login-action@v3
         with:
           username: ${{ secrets.DOCKER_USERNAME }}