Bumper: fix case where target is up to date (#917)

.github/workflows/bumper.yml

@@ -24,13 +24,14 @@ jobs:
           repository: ${{ matrix.target.repo }}
           ref: ${{ matrix.target.branch }}
           path: nbc
-          submodules: true
           fetch-depth: 0
           token:  ${{ secrets.ACTIONS_GITHUB_TOKEN }}
 
       - name: Checkout this ref
         run: |
-          cd nbc/vendor/nim-libp2p
+          cd nbc
+          git submodule update --init vendor/nim-libp2p
+          cd vendor/nim-libp2p
           git checkout $GITHUB_SHA
 
       - name: Commit this bump
@@ -38,7 +39,7 @@ jobs:
           cd nbc
           git config --global user.email "${{ github.actor }}@users.noreply.github.com"
           git config --global user.name = "${{ github.actor }}"
-          git commit -a -m "auto-bump nim-libp2p"
+          git commit --allow-empty -a -m "auto-bump nim-libp2p"
           git branch -D nim-libp2p-auto-bump-${GITHUB_REF##*/} || true
           git switch -c nim-libp2p-auto-bump-${GITHUB_REF##*/}
           git push -f origin nim-libp2p-auto-bump-${GITHUB_REF##*/}