ci: stop doing updates on feature branches

.github/workflows/bump.yml

@@ -8,6 +8,9 @@ jobs:
     name: Bump Browser Versions
     runs-on:
       ubuntu-22.04
+    env:
+      # https://stackoverflow.com/a/71158878/2014893
+      BRANCH_NAME: ${{ github.head_ref || github.ref_name }}
     steps:
       - name: git checkout
         uses: actions/checkout@v4
@@ -30,13 +33,17 @@ jobs:
         run: |
           set -e
           git fetch
-          git checkout main
           git config --global user.name 'BumpBot'
           git config --global user.email '[email protected]'
       - name: update google-chrome
         run: |
-          nix develop --command \
-            ./google-chrome/update.py --commit
+          echo branch_name is "$BRANCH_NAME"
+          if [[ "$BRANCH_NAME" == "main" ]]; then
+            nix develop --command \
+              ./google-chrome/update.py --commit
+          else
+            echo "not on branch 'main'; skipping update.py."
+          fi
       - name: check build outputs
         env:
           NIXPKGS_ALLOW_UNFREE: "1"