Update .editorconfig for thread synchronization preference

Added suggestion to prefer System.Threading.Lock for thread synchronization in C#.

Author: AngeloDotNet

.editorconfig

@@ -131,6 +131,7 @@ csharp_prefer_braces = true:silent
 csharp_prefer_simple_using_statement = true:suggestion
 csharp_style_namespace_declarations = file_scoped:suggestion
 csharp_style_prefer_method_group_conversion = true:silent
+csharp_prefer_system_threading_lock = true:suggestion
 
 # Expression-level preferences
 csharp_prefer_simple_default_expression = true:suggestion