fix: update toString() params

1) CodeIgniter\Database\DatabaseTestCase\DatabaseTestCaseMigrationOnce1Test::testMigrationDone
TypeError: json_encode(): Argument #2 ($flags) must be of type int, bool given

/home/runner/work/CodeIgniter4/CodeIgniter4/system/Test/Constraints/SeeInDatabase.php:118
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Test/DatabaseTestTrait.php:282
/home/runner/work/CodeIgniter4/CodeIgniter4/tests/system/Database/DatabaseTestCase/DatabaseTestCaseMigrationOnce1Test.php:86

system/Test/Constraints/SeeInDatabase.php

@@ -67,7 +67,7 @@ protected function failureDescription($table): string
         return sprintf(
             "a row in the table [%s] matches the attributes \n%s\n\n%s",
             $table,
-            $this->toString(JSON_PRETTY_PRINT),
+            $this->toString(false, JSON_PRETTY_PRINT),
             $this->getAdditionalInfo($table)
         );
     }
@@ -113,7 +113,7 @@ protected function getAdditionalInfo(string $table): string
      *
      * @param int $options
      */
-    public function toString($options = 0): string
+    public function toString(bool $exportObjects = false, $options = 0): string
     {
         return json_encode($this->data, $options);
     }