Fix IPv6 URL when trying to fetch challenge ourselves for debugging

Fixes the following error when debugging is enabled:

[Sat Feb 21 04:00:22 CET 2026] Here is the curl dump log:
[Sat Feb 21 04:00:22 CET 2026] * URL rejected: Port number was not a decimal number between 0 and 65535
* closing connection #-1

IPv6 addresses in URLs need to be written like this:

    http://[2001:43:5::250]

Author: pgerber

acme.sh

@@ -5181,7 +5181,12 @@ $_authorizations_map"
         if [ "$DEBUG" ]; then
           if [ "$vtype" = "$VTYPE_HTTP" ]; then
             _debug "Debug: GET token URL."
-            _get "http://$d/.well-known/acme-challenge/$token" "" 1
+            if _isIPv6 "$d"; then
+                host="[$d]"
+            else
+                host="$d"
+            fi
+            _get "http://$host/.well-known/acme-challenge/$token" "" 1
           fi
         fi
         _clearupwebbroot "$_currentRoot" "$removelevel" "$token"