[Minor] Properly make use of selectors for checking MID RHSs against DNSBLs

Related to: https://github.com/rspamd/rspamd/pull/4888

conf/modules.d/rbl.conf

@@ -208,7 +208,9 @@ rbl {
       checks = ['emails', 'dkim', 'helo', 'rdns', 'replyto', 'urls'];
       emails_domainonly = true;
       exclude_users = false;
-      selector = 'header(Message-Id).regexp("@([^\.]+\.[^>]+)").last';
+      selector = {
+        mid = 'header(Message-Id).regexp("@([^\.]+\.[^>]+)").last';
+      }
 
       returnbits = {
         CRACKED_SURBL = 128;
@@ -245,7 +247,9 @@ rbl {
       checks = ['emails', 'dkim', 'helo', 'rdns', 'replyto', 'urls'];
       emails_domainonly = true;
       exclude_users = false;
-      selector = 'header(Message-Id).regexp("@([^\.]+\.[^>]+)").last';
+      selector = {
+        mid = 'header(Message-Id).regexp("@([^\.]+\.[^>]+)").last';
+      }
 
       returnbits {
         URIBL_BLOCKED = 1;
@@ -279,7 +283,9 @@ rbl {
       checks = ['emails', 'dkim', 'helo', 'rdns', 'replyto', 'urls'];
       emails_domainonly = true;
       exclude_users = false;
-      selector = 'header(Message-Id).regexp("@([^\.]+\.[^>]+)").last';
+      selector = {
+        mid = 'header(Message-Id).regexp("@([^\.]+\.[^>]+)").last';
+      }
 
       returncodes = {
         # spam domain