LOCAL:Maniphest:Apply approver rule to event type

Replicate the logic to auto-fill approver for `event` subtype.

Until now event and purchasing forms used the same template but
they were split in two - `purchasing` and `event` - after the
Snipe-IT integration that applied major changes in the purchasing
request form.

src/applications/maniphest/editor/ManiphestTransactionEditor.php

@@ -479,6 +479,15 @@ final class ManiphestTransactionEditor
               }
               break;
 
+            case 'std:maniphest:event:project':
+              foreach ($xaction->getRequiredHandlePHIDs() as $p) {
+                if (!empty($p)) {
+                  $purchasing_project = $p;
+                  break;
+                }
+              }
+              break;
+
             case 'std:maniphest:sysadmin:confidential-request':
               if ($xaction->getNewValue() != $xaction->getOldValue()) {
                 $changed_confidentiality = true;
@@ -545,11 +554,11 @@ final class ManiphestTransactionEditor
       }
     }
 
-    // CCU: If this is a purchasing type, then try to assign the task to the
-    //      assignee, if empty. It's not overlay pleasant code, since we need
+    // CCU: If this is a purchasing or event type, then try to assign the task to
+    //      the assignee, if empty. It's not overlay pleasant code, since we need
     //      to iterate the transactions, rather than interrogate an object.
     if ($this->getIsNewObject() && !$any_assign) {
-      if ($subtype == 'purchasing') {
+      if (in_array($subtype, array('purchasing', 'event'))) {
         if ($approver == null && $purchasing_project !== null) {
           $p_proj = id(new PhabricatorProjectQuery())
             ->setViewer($this->getActor())