dev/pr-auditor: fix discarding events against unknown base refs
Created by: bobheadxi
Missed return. See https://github.com/sourcegraph/sec-pr-audit-trail/issues/142#issuecomment-1081721136
Test plan
n/a
Created by: bobheadxi
Missed return. See https://github.com/sourcegraph/sec-pr-audit-trail/issues/142#issuecomment-1081721136
n/a