Fix test_seqscans on remote cluster (#2869)

A remote project is reused between tests, so we need to ensure that we
don't have a table with the same name already created.

test_runner/performance/test_seqscans.py

@@ -33,6 +33,7 @@ from pytest_lazyfixture import lazy_fixture  # type: ignore
 def test_seqscans(env: PgCompare, rows: int, iters: int, workers: int):
     with closing(env.pg.connect()) as conn:
         with conn.cursor() as cur:
+            cur.execute("drop table if exists t;")
             cur.execute("create table t (i integer);")
             cur.execute(f"insert into t values (generate_series(1,{rows}));")