update php8 string function (#38071)

Author: shuvroroy

src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php

@@ -702,8 +702,8 @@ protected function serializeClassCastableAttribute($key, $value)
      */
     protected function isCustomDateTimeCast($cast)
     {
-        return strncmp($cast, 'date:', 5) === 0 ||
-               strncmp($cast, 'datetime:', 9) === 0;
+        return str_starts_with($cast, 'date:') ||
+                str_starts_with($cast, 'datetime:');
     }
 
     /**
@@ -714,7 +714,7 @@ protected function isCustomDateTimeCast($cast)
      */
     protected function isDecimalCast($cast)
     {
-        return strncmp($cast, 'decimal:', 8) === 0;
+        return str_starts_with($cast, 'decimal:');
     }
 
     /**