bug(flakey test): fix assertion (#100643)

found through https://sentry.sentry.io/issues/6856563923/ and
https://sentry.sentry.io/issues/6864905942/
assertion is definitely a typo and would pass in most situations, making
this look flakey.
Fixed the test so it is asserting on the correct value, didn't see this
typo elsewhere in code.

Author: nora-shap

tests/sentry/mail/test_adapter.py

@@ -868,7 +868,7 @@ def test_notify_with_suspect_commits(self) -> None:
 
         assert "Suspect Commits" in msg.body
         assert self.user.email in msg.body
-        assert commit.key[-7] in msg.body
+        assert commit.key[:7] in msg.body
 
     def test_notify_with_replay_id(self) -> None:
         project = self.project