Add automount.cgroups to WSL_CONF_KEYS in validate-modern.py (#14285)

Fixes #13993

The validate-modern.py script was missing the 'automount.cgroups' setting
from WSL_CONF_KEYS, causing validation errors when distributions include
this setting in their /etc/wsl.conf files.

Note: windowsterminal.enabled was already present in the
wsl-distribution.conf validation list.

Co-authored-by: Ben Hillis <benhill@ntdev.microsoft.com>

Author: benhillis

distributions/validate-modern.py

@@ -39,7 +39,8 @@
 
 WSL1_UNSUPPORTED_XATTRS = ['security.selinux', 'security.ima', 'security.evm']
 
-WSL_CONF_KEYS = ['automount.enabled',
+WSL_CONF_KEYS = ['automount.cgroups',
+                 'automount.enabled',
                  'automount.ldconfig',
                  'automount.mountfstab',
                  'automount.options',