Fix PHPUnit 8 warnings

The `assertArraySubset` method has been deprecated and the
`assertContains` method should no longer be used with strings.

This alternatives suppress the warnings.

tests/Watchers/DumpWatcherTest.php

@@ -28,6 +28,6 @@ public function test_dump_watcher_register_entry()
         $entry = $this->loadTelescopeEntries()->first();
 
         $this->assertSame(EntryType::DUMP, $entry->type);
-        $this->assertContains($var, $entry->content['dump']);
+        $this->assertStringContainsString($var, $entry->content['dump']);
     }
 }

tests/Watchers/EventWatcherTest.php

@@ -45,7 +45,9 @@ public function test_event_watcher_stores_payloads()
         $this->assertSame(EntryType::EVENT, $entry->type);
         $this->assertSame(DummyEvent::class, $entry->content['name']);
         $this->assertArrayHasKey('data', $entry->content['payload']);
-        $this->assertArraySubset(['Telescope', 'Laravel', 'PHP'], $entry->content['payload']['data']);
+        $this->assertContains('Telescope', $entry->content['payload']['data']);
+        $this->assertContains('Laravel', $entry->content['payload']['data']);
+        $this->assertContains('PHP', $entry->content['payload']['data']);
     }
 }
 

tests/Watchers/MailWatcherTest.php

@@ -41,7 +41,7 @@ public function test_mail_watcher_registers_entry()
         $this->assertSame(['bcc@laravel.com'], array_keys($entry->content['bcc']));
         $this->assertSame('Check this out!', $entry->content['subject']);
         $this->assertSame('Telescope is amazing!', $entry->content['html']);
-        $this->assertContains('Telescope is amazing!', $entry->content['raw']);
+        $this->assertStringContainsString('Telescope is amazing!', $entry->content['raw']);
         $this->assertEmpty($entry->content['replyTo']);
     }
 }

tests/Watchers/NotificationWatcherTest.php

@@ -32,7 +32,7 @@ public function test_notification_watcher_registers_entry()
         $this->assertSame(EntryType::NOTIFICATION, $entry->type);
         $this->assertSame(BoomerangNotification::class, $entry->content['notification']);
         $this->assertSame(false, $entry->content['queued']);
-        $this->assertContains('telescope@laravel.com', $entry->content['notifiable']);
+        $this->assertStringContainsString('telescope@laravel.com', $entry->content['notifiable']);
         $this->assertSame('mail', $entry->content['channel']);
         $this->assertNull($entry->content['response']);
     }