Merge branch '7.1' into 7.2

* 7.1:
  Remove comment about AppVeyor in `phpunit`
  [Webhook][RemoteEvent] fix SendgridPayloadConverter category support
  Update old Appveyor skip conditions
  sync the Dutch translation file with changes from the 7.2 branch
  [Yaml] fix inline notation with inline comment
  fix(property-info): make sure that SerializerExtractor returns null for invalid class metadata
  [RemoteEvent][Webhook] fix SendgridRequestParser & SendgridPayloadConverter in case of missing sg_message_id
  fix_50486 - memory leak

Author: xabbuh

Resources/translations/validators.nl.xlf

@@ -466,6 +466,10 @@
                 <source>This value should not be after week "{{ max }}".</source>
                 <target>Deze waarde mag niet na week "{{ max }}" liggen.</target>
             </trans-unit>
+            <trans-unit id="120">
+                <source>This value is not a valid slug.</source>
+                <target state="needs-review-translation">Deze waarde is geen geldige slug.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>