Fix bash syntax for creating a variable

.drone.yml

@@ -42,7 +42,7 @@ steps:
   - name: docker build and push
     image: docker:24.0.7
     commands:
-      - $dockerImageWithTag = "$docker_registry$docker_repo:$DRONE_BRANCH"
+      - dockerImageWithTag="$docker_registry$docker_repo:$DRONE_BRANCH"
       - docker build . -t $dockerImageWithTag
       - echo $docker_password | docker login --username $docker_username --password-stdin $docker_registry
       - docker push $dockerImageWithTag