change repoRev.IndexedHEADCommit to method call
Created by: ijt
This is to fix a broken build. See https://buildkite.com/sourcegraph/sourcegraph/builds/41169#9c89a67d-8f43-4a2a-b149-75fc3e16b593.
Test plan: run tests in graphqlbackend dir.
Created by: ijt
This is to fix a broken build. See https://buildkite.com/sourcegraph/sourcegraph/builds/41169#9c89a67d-8f43-4a2a-b149-75fc3e16b593.
Test plan: run tests in graphqlbackend dir.