coverage: Skip zerver.lib.migrate coverage.

It is only covered when we run migration tests, which we are not
guaranteed to always be able to do.

tools/test-backend

@@ -122,6 +122,9 @@ not_yet_fully_covered = [
     # Cannot have coverage, as tests run in a transaction
     "zerver/lib/safe_session_cached_db.py",
     "zerver/lib/singleton_bmemcached.py",
+    # Only covered when we run migrations tests, which are not
+    # guaranteed to exist or be runnable
+    "zerver/lib/migrate.py",
     # Branches in Django settings files are hard to test
     "zproject/computed_settings.py",
     "zproject/dev_settings.py",

zerver/lib/migrate.py

@@ -11,7 +11,7 @@ def do_batch_update(
     assignments: List[Composable],
     batch_size: int = 10000,
     sleep: float = 0.1,
-) -> None:  # nocoverage
+) -> None:
     # The string substitution below is complicated by our need to
     # support multiple PostgreSQL versions.
     stmt = SQL(