Address some PHP 8.1 deprecation notices

- Replace a strstr call by strpos in Model\APContact
- Simplify conditions in Protocol\DFRN
- Address part of https://github.com/friendica/friendica/issues/12011#issuecomment-1331012289

src/Navigation/Notifications/ValueObject/Introduction.php

@@ -226,6 +226,7 @@ class Introduction implements \JsonSerializable
 	/**
 	 * @inheritDoc
 	 */
+	#[\ReturnTypeWillChange]
 	public function jsonSerialize()
 	{
 		return $this->toArray();