Update publish.yml to quote env vars

Author: cboulay

.github/workflows/publish.yml

@@ -18,7 +18,7 @@ jobs:
         env:
           HOMEBREW_GITHUB_API_TOKEN: ${{ github.token }}
           PULL_REQUEST: ${{ github.event.pull_request.number }}
-        run: brew pr-pull --debug --tap=$GITHUB_REPOSITORY $PULL_REQUEST
+        run: brew pr-pull --debug --tap="$GITHUB_REPOSITORY" "$PULL_REQUEST"
 
       - name: Push commits
         uses: Homebrew/actions/git-try-push@master
@@ -30,4 +30,4 @@ jobs:
         if: github.event.pull_request.head.repo.fork == false
         env:
           BRANCH: ${{ github.event.pull_request.head.ref }}
-        run: git push --delete origin $BRANCH
+        run: git push --delete origin "$BRANCH"