fix(bots): Fix some system messages for bots

[nickvergessen]

🏚️ Before

[error] 2023-08-18T16:18:59.000 no app in contex Call to a member function isGuest() on null in file '…/lib/Chat/Parser/SystemMessage.php' line 281     

🏡 After

[debug] 2023-08-18T16:23:04.000 call_summary_bot {"type":"Activity","actor":{"type":"Person","id":"users\/admin","name":"Laura Adams"},"object":{"type":"Note","id":"2165","name":"user_added","content":"{\"message\":\"{actor} added {user}\",\"parameters\":{\"actor\":{\"type\":\"user\",\"id\":\"admin\",\"name\":\"Laura Adams\"},\"user\":{\"type\":\"us│

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not required
• 📘 API documentation in docs/ has been updated or is not required
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required
• 🔖 Capability is added or not needed

[nickvergessen]

Force pushed with:

diff --git a/tests/php/Chat/Parser/SystemMessageTest.php b/tests/php/Chat/Parser/SystemMessageTest.php
index c7b8369c5..e615b36a3 100644
--- a/tests/php/Chat/Parser/SystemMessageTest.php
+++ b/tests/php/Chat/Parser/SystemMessageTest.php
@@ -461,7 +461,7 @@ class SystemMessageTest extends TestCase {
        public function testParseMessage(string $message, array $parameters, ?string $recipientId, string $expectedMessage, array $expectedParameters) {
                /** @var Participant|MockObject $participant */
                $participant = $this->createMock(Participant::class);
-               if ($recipientId  === null) {
+               if ($recipientId === null) {
                        $participant = null;
                } elseif ($recipientId && strpos($recipientId, 'guest::') !== false) {
                        $attendee = Attendee::fromRow([

[nickvergessen]

/backport to stable27