chore(sqlalchemy-bigquery): restore complete coverage (#17770)

This PR restores coverage for sqlalchemy-bigquery

Towards #17459 🦕

Author: ohmayr

packages/sqlalchemy-bigquery/.coveragerc

@@ -22,7 +22,7 @@ omit =
   sqlalchemy_bigquery/requirements.py
 
 [report]
-fail_under = 98
+fail_under = 100
 show_missing = True
 exclude_lines =
     # Re-enable the standard pragma
@@ -37,3 +37,5 @@ omit =
   */core/*.py
   */site-packages/*.py
   sqlalchemy_bigquery/requirements.py
+  tests/*
+  */tests/*

packages/sqlalchemy-bigquery/tests/unit/test_engine.py

@@ -70,3 +70,9 @@ def test_arraysize_querystring_takes_precedence_over_default(faux_conn, metadata
     metadata.create_all(engine)
 
     assert conn.connection.test_data["arraysize"] == arraysize
+
+
+def test_dbapi_deprecated():
+    from sqlalchemy_bigquery.base import BigQueryDialect
+
+    assert BigQueryDialect.dbapi() is BigQueryDialect.import_dbapi()