fix merge queue ci (#10090)

Previously, merge groups would try to compare protobuf against the
previous merge queue commit. However, it’s not yet possible to do that
comparison.

Instead, compare all ongoing merge queue commits against master, rather
than against the commit just before them.

.github/workflows/ci.yml

@@ -96,7 +96,7 @@ jobs:
       - uses: bufbuild/buf-setup-action@1158f4fa81bc02e1ff62abcca6d516c9e24c77da
       - uses: bufbuild/buf-breaking-action@a074e988ee34efcd4927079e79c611f428354c01
         with:
-          against: "https://github.com/near/nearcore.git#ref=${{ github.event.pull_request.base.sha || github.event.merge_group.base_sha }}"
+          against: "https://github.com/near/nearcore.git#${{github.event.pull_request.base.sha && format('ref={0}', github.event.pull_request.base.sha) || 'branch=master' }}"
 
   sanity_checks:
     name: "Sanity Checks"