`RetriggerBodhiUpdateHandler` should handle the cases where there is no build in stable tags

[majamassarini]

This is the sentry issue.

I want to release Packit in EPEL 10 from side tags. It is expected that Packit won't be in a stable tag yet, and the retriggering handler should handle this case when the update will happen from the side tags, because the build will be found in the side tag itself.

This issue blocks the bodhi updates of packit package in epel10.

[nforro]

The problem here is that there is a single RetriggerBodhiUpdateHandler that handles both sidetag and regular updates. But it inherits from GetKojiBuildDataFromKojiServiceMixin that always searches for the latest candidate build to add to a non-sidetag update. If the search doesn't end with an error, it works, the search result is ignored and sidetag handling proceeds. But if it ends with an error, we have a problem even though we don't care about the result.