internal/database: fix benchmark

Drop the table only if it exists.

Change-Id: Id2d772fade7ab2624c6a155d0985f09284c734e4
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/304629
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
diff --git a/internal/database/benchmark_test.go b/internal/database/benchmark_test.go
index c3b1e62..924880a 100644
--- a/internal/database/benchmark_test.go
+++ b/internal/database/benchmark_test.go
@@ -24,7 +24,7 @@
 	}
 	defer pgxDB.Close()
 
-	if _, err := testDB.Exec(ctx, `DROP TABLE test_large_bulk; CREATE TABLE test_large_bulk (i BIGINT);`); err != nil {
+	if _, err := testDB.Exec(ctx, `DROP TABLE IF EXISTS test_large_bulk; CREATE TABLE test_large_bulk (i BIGINT);`); err != nil {
 		b.Fatal(err)
 	}
 	const size = 15000