Fix check_commit jobs on 0.1 branch

Author: tnull

.github/workflows/build.yml

@@ -198,9 +198,9 @@ jobs:
           git fetch upstream
           export GIT_COMMITTER_EMAIL="rl-ci@example.com"
           export GIT_COMMITTER_NAME="RL CI"
-          git rebase upstream/main
+          git rebase upstream/0.1
       - name: For each commit, run cargo check (including in fuzz)
-        run: ci/check-each-commit.sh upstream/main
+        run: ci/check-each-commit.sh upstream/0.1
 
   check_release:
     runs-on: ubuntu-latest