Fix env variable usage in e2e workflow (#58)

.github/workflows/e2e.yaml

@@ -42,7 +42,7 @@ jobs:
         # TODO: Any nicer way to do this? :P
         - name: Set Tags
           run: |
-            echo "COMMIT_TAG=${{ matrix.docker-images.name }}:${{ SHORT_SHA }}" >> $GITHUB_ENV
+            echo "COMMIT_TAG=${{ matrix.docker-images.name }}:${{ env.SHORT_SHA }}" >> $GITHUB_ENV
             if [ "${{ github.ref }}" = "refs/heads/main" ]; then
               echo "LATEST_TAG=${{ matrix.docker-images.name }}:latest" >> $GITHUB_ENV
             else
@@ -56,8 +56,8 @@ jobs:
             context: . # Even though the docker images are in the testing directory, they need the root context
             file: ${{ matrix.docker-images.path }}
             tags: |
-              ${{ COMMIT_TAG }}
-              ${{ LATEST_TAG }}
+              ${{ env.COMMIT_TAG }}
+              ${{ env.LATEST_TAG }}
 
   e2e:
     name: "E2E test"