fix flaky test. (#1663)

TestIssue1567 fails by max_connections error. This makes our CI unhappy.

https://github.com/go-sql-driver/mysql/actions/runs/12904961433/job/35984402310

Author: methane

driver_test.go

@@ -3608,6 +3608,12 @@ func runCallCommand(dbt *DBTest, query, name string) {
 func TestIssue1567(t *testing.T) {
 	// enable TLS.
 	runTests(t, dsn+"&tls=skip-verify", func(dbt *DBTest) {
+		var max int
+		err := dbt.db.QueryRow("SELECT @@max_connections").Scan(&max)
+		if err != nil {
+			dbt.Fatalf("%s", err.Error())
+		}
+
 		// disable connection pooling.
 		// data race happens when new connection is created.
 		dbt.db.SetMaxIdleConns(0)
@@ -3627,6 +3633,9 @@ func TestIssue1567(t *testing.T) {
 		if testing.Short() {
 			count = 10
 		}
+		if count > max {
+			count = max
+		}
 
 		for i := 0; i < count; i++ {
 			timeout := time.Duration(mrand.Int63n(int64(rtt)))