Fix sudo::defaults function to correctly place list - #338

I was using this module on a new Debian 13 host and checked the changes to the default sudoers file.
Reviewing the changes I wanted to preserve some of the defaults. However, most of the Debian defaults are specified like `Defaults:%sudo ...`. Therefore I tried using the `list` value with `:%sudo`. As this was placed after the key and not directly after `Defaults` it led to an error in the sudoers configuration:
~~~
/etc/sudoers:4:18: syntax error
Defaults env_keep:%sudo+="http_proxy https_proxy ftp_proxy all_proxy no_proxy"
 ^~~~~~~
~~~
I'm not entirely sure what the `list` key does in the current form but I think it needs to go directly after the `Defaults` string, as indicated by `man sudoers`. With this change the resulting sudoers file works correctly:
~~~
Defaults:%sudo env_keep+="http_proxy https_proxy ftp_proxy all_proxy no_proxy"
~~~