PullRequestService.searchByCommit should require same permission as PullRequestService.search

Problem

When a plugin job executor calls PullRequestService.searchByCommit, the call throws an exception because it requires an authenticated user. Escalating privileges with SecurityService.withPermission(Permission.REPO_READ, "reason") isn't enough.

A roughly similar call, PullRequestService.search does not require an authenticated user. searchByCommit applies stricter security predicates.

Proposed solution

Apply the same security predicate in  PullRequestService.searchByCommit as PullRequestService.search.