fix: don't close DB connection after it's established (#49)

The docs for DB.Close() specfically say not to do this. These
connections should be long-lived. This bug may be causing problems with
connection pooling, causing clients to get "bad connection" errors.

mysqltest/docker.go

@@ -159,7 +159,6 @@ func tryLogin(conf *config, port string) error {
 	if err != nil {
 		return fmt.Errorf("sql.Open(): %w", err)
 	}
-	defer db.Close()
 
 	if err := db.Ping(); err != nil {
 		return fmt.Errorf("db.Ping(): %w", err)

mysqltest/docker_test.go

@@ -46,7 +46,6 @@ func TestKillAfter(t *testing.T) {
 		t.Fatal(err)
 	}
 	db := connect(t, ci)
-	defer db.Close()
 
 	if err := db.Ping(); err != nil {
 		t.Fatalf("db.Ping: %v", err)