check-certificates: match status code in error message

The message used to be:

    Fetch failed with status 404

... but changed recently:

    failure: Status 404, NOT FOUND

The new string is in RouterOS 7.22, and changed in what ever
beta or rc release. Let's just match the status code and hope
for the best.

check-certificates.rsc

@@ -60,7 +60,7 @@
               http-header-field=({ [ $FetchUserAgentStr $ScriptName ] }) \
               ($CertRenewUrl . $CertFileName) dst-path=$CertFileName as-value;
         } do={
-          :if ($Err != "Fetch failed with status 404") do={
+          :if (!($Err ~ "[Ss]tatus 404")) do={
             $LogPrint warning $0 ("Failed fetching certificate: " . $Err);
           }
           :error false;