policy: pushing invalidates PR approval

Signed-off-by: Jakob Borg <jakob@kastelo.net>

.policy.yml

@@ -53,6 +53,7 @@ approval_rules:
     options:
       ignore_update_merges: true
       allow_non_author_contributor: true
+      invalidate_on_push: true
 
   # Regular pull requests require approval by an active contributor
   - name: is approved by a syncthing contributor
@@ -63,6 +64,7 @@ approval_rules:
     options:
       ignore_update_merges: true
       allow_non_author_contributor: true
+      invalidate_on_push: true
 
   # Changes to some files (translations, dependencies, compatibility) do not
   # require approval if they were proposed by a contributor and have a