Perforce is a bit of a special duck because it needs to use p4 for all communication with the code host, unlike most/all other sources, which can use HTTP(S) to communicate with the code host

The discussion in PR #56697 made it clear that PerforceSource should not assume the availability of p4. #56697 changed the behavior of CheckConnection; now ListRepos needs similar attention. Currently it uses PerforceDepotSyncer, which uses p4 directly. ListRepos may not be used in the same way that `CheckConnection1 is, so it may be ok with this behavior, but it bears examining.