Changed way to use variables (set locally and later in github_env)

.github/workflows/gitlab_ci.yml

@@ -89,10 +89,10 @@ jobs:
           git checkout "${{ github.base_ref }}"
           echo "Git pull"
           git pull
-          echo "New branch shall be named: TEMPORARY_MERGE_PR_${{ github.event.number }}"
-          echo "MIRROR_BRANCH=TEMPORARY_MERGE_PR_$github.event.number" >> $GITHUB_ENV
-          echo "Create new branch ${{ env.MIRROR_BRANCH }} and check it out"
-          git checkout -b "${{ env.MIRROR_BRANCH }}"
+          MIRROR_BRANCH="TEMPORARY_MERGE_PR_${{ github.event.number }}"
+          echo MIRROR_BRANCH="$MIRROR_BRANCH" >> $GITHUB_ENV
+          echo "Create new branch $MIRROR_BRANCH and check it out"
+          git checkout -b "$MIRROR_BRANCH"
           git merge --ff-only "${{ github.event.pull_request.head.sha }}"
       - name: Mirror and wait for Gitlab-CI
         uses: jakob-fritz/github2lab_action@Iss37_variable_for_checkout