workflow: --dry-run for the deploy.yml debut (see #397)

.github/workflows/deploy.yml

@@ -16,8 +16,6 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-      with:
-        ref: 'v3.3.1'
     - name: Clone repository
       working-directory: build
       env:
@@ -39,4 +37,4 @@ jobs:
         git config --local user.name "$GITHUB_ACTOR"
         git add $FORMULA
         git commit -m "Update to ${{ github.ref }}"
-        git push origin master
+        git push --dry-run origin master