Remove hardcoded line number in Loguru tests

[szokeasaurusrex]

It's kinda gonna be a pain to maintain this if we might add/remove imports in the future. Perhaps we could just check that the value here is an int? Or maybe there is some fancy introspection logic we could use to compute the line?

We can also address this in a separate PR, I guess it's not exactly in scope here to fix

Originally posted by @szokeasaurusrex in https://github.com/getsentry/sentry-python/pull/4445#discussion_r2137254102