build: fix variable syntax

.gitea/workflows/deploy.yml

@@ -32,9 +32,10 @@ jobs:
           pip install --no-cache-dir -r requirements.txt
 
       - name: Setup content directory for year branches
+        env:
+          BRANCH_NAME: $${{ vars.GITEA_REF_NAME}}
         if: gitea.ref != 'refs/heads/master'
         run: |
-          BRANCH_NAME=${{vars.GITEA_REF_NAME}}
           echo "Branch name: $BRANCH_NAME"
           echo "Testing URL: https://git.opytex.org/Cours/${BRANCH_NAME}.git"
           curl -I "https://git.opytex.org/Cours/${BRANCH_NAME}.git" || echo "URL not accessible"