Fix default value for <select /> standard custom fields

Summary: We aren't setting the value for select fields correctly, so when
editing they always show the first value instead of the correct value.

Test Plan: Set task from Apple -> Banana and Carrot -> Potato, saved, hit
"Edit", saw Banana / Potato.

Auditors: btrahan

src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldSelect.php

@@ -69,6 +69,7 @@ final class PhabricatorStandardCustomFieldSelect
       ->setLabel($this->getFieldName())
       ->setCaption($this->getCaption())
       ->setName($this->getFieldKey())
+      ->setValue($this->getFieldValue())
       ->setOptions($this->getOptions());
   }