refactor: fix TypeError in BaseConnection

1) CodeIgniter\Models\InsertModelTest::testInsertPermitInsertNoData
TypeError: strcspn(): Argument #1 ($string) must be of type string, int given

/home/runner/work/CodeIgniter4/CodeIgniter4/system/Database/BaseConnection.php:1042
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Database/BaseConnection.php:1029
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Model.php:308
/home/runner/work/CodeIgniter4/CodeIgniter4/system/BaseModel.php:782
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Model.php:707
/home/runner/work/CodeIgniter4/CodeIgniter4/tests/system/Models/InsertModelTest.php:255

Author: kenjis

system/Database/BaseConnection.php

@@ -1006,10 +1006,10 @@ public function getConnectDuration(int $decimals = 6): string
      * insert the table prefix (if it exists) in the proper position, and escape only
      * the correct identifiers.
      *
-     * @param array|string $item
-     * @param bool         $prefixSingle       Prefix a table name with no segments?
-     * @param bool         $protectIdentifiers Protect table or column names?
-     * @param bool         $fieldExists        Supplied $item contains a column name?
+     * @param array|int|string $item
+     * @param bool             $prefixSingle       Prefix a table name with no segments?
+     * @param bool             $protectIdentifiers Protect table or column names?
+     * @param bool             $fieldExists        Supplied $item contains a column name?
      *
      * @return array|string
      * @phpstan-return ($item is array ? array : string)
@@ -1030,6 +1030,9 @@ public function protectIdentifiers($item, bool $prefixSingle = false, ?bool $pro
             return $escapedArray;
         }
 
+        // If you pass `['column1', 'column2']`, `$item` will be int because the array keys are int.
+        $item = (string) $item;
+
         // This is basically a bug fix for queries that use MAX, MIN, etc.
         // If a parenthesis is found we know that we do not need to
         // escape the data or add a prefix. There's probably a more graceful