Fix the variable in the code-check workflow

.github/workflows/code-check.yml

@@ -22,7 +22,7 @@ jobs:
     name: Check the code
     runs-on: ubuntu-latest
     env:
-      DOCKER_IMAGE=publishpress/dev-workspace-terminal:future-free-2
+      DOCKER_IMAGE: publishpress/dev-workspace-terminal:future-free-2
 
     steps:
       - name: Setup tmate session for Debugging, if inputs.debug_enabled_code_check is true
@@ -47,8 +47,8 @@ jobs:
       - if: steps.image-cache.outputs.cache-hit != 'true'
         name: Pull Docker image
         run: |
-          docker pull DOCKER_IMAGE
-          docker save -o ~/image-cache/terminal.tar DOCKER_IMAGE
+          docker pull $DOCKER_IMAGE
+          docker save -o ~/image-cache/terminal.tar $DOCKER_IMAGE
 
       - if: steps.image-cache.outputs.cache-hit == 'true'
         name: Load Docker image from cache
@@ -59,5 +59,5 @@ jobs:
           docker run --rm -it \
             -v ${{ github.workspace }}:/project \
             --workdir="/project" \
-            DOCKER_IMAGE \
+            $DOCKER_IMAGE \
             bash -c "composer validate && composer install --no-interaction --no-progress --prefer-dist --ignore-platform-reqs && composer check"