[C#] Simplify regex argument push

Co-authored-by: deathaxe <16542113+deathaxe@users.noreply.github.com>

Author: michaelblyons

C#/C#.sublime-syntax

@@ -2164,8 +2164,7 @@ contexts:
 
   regex_arguments:
     - match: (?=[@$]*")
-      push:
-        - include: regex_string
+      push: regex_string
     - include: arguments
 
   arguments: