Deal with possibility that HTTP_REFERER is not in array
We have had a couple of sites with notices like
Thu Jul 11 02:00:22.027594 2024] [php:warn] [pid 22552] [client 2a03:2880:27ff:a::face:b00c:43428] PHP Warning: Undefined array key "HTTP_REFERER" in /<client site>/wp-content/uploads/civicrm/ext/reporterror/CRM/ReportError/Handler/FormsNoReferer.php on line 28
I believe this should resolve such notices