github: check commits against base branch

.github/workflows/main.yml

@@ -116,16 +116,16 @@ jobs:
         with:
           go-version: '${{ env.GO_VERSION }}'
 
-      - name: fetch and rebase on master
+      - name: fetch and rebase on ${{ github.base_ref }}
         run: |
-          git remote add upstream https://github.com/lightningnetwork/lnd
+          git remote add upstream https://github.com/${{ github.repository }}
           git fetch upstream
           export GIT_COMMITTER_EMAIL="lnd-ci@example.com"
           export GIT_COMMITTER_NAME="LND CI"
-          git rebase upstream/master
+          git rebase upstream/${{ github.base_ref }}
 
       - name: check commits
-        run: scripts/check-each-commit.sh upstream/master
+        run: scripts/check-each-commit.sh upstream/${{ github.base_ref }}
 
   ########################
   # lint code