fix(test): wait for MariaDB with the root password, not the init window

The entrypoint installs root@localhost without unix_socket auth and sets
its password during init, so the passwordless socket probe only passed
when it landed in the window before SET PASSWORD. Missing that window
timed the e2e MariaDB suites out at random.

The probe now authenticates with the root password it already received
and requires @@skip_networking = 0, so the entrypoint's temporary server
no longer counts as ready. The anonymous-preemption bootstrap logs in
with the root password as well.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/e2e/test_e2e_mariadb_anonymous_preemption.py

@@ -100,7 +100,10 @@ class TestE2EMariaDBAnonymousPreemption(unittest.TestCase):
                 cls.db_container,
                 "sh",
                 "-lc",
-                f'mariadb -uroot --protocol=socket -e "{bootstrap_sql}"',
+                (
+                    f"mariadb -uroot -p{cls.root_password} --protocol=socket "
+                    f'-e "{bootstrap_sql}"'
+                ),
             ]
         )