Update caller-argument-expression.md for improved syntax highlighting (#7211)

Incorrect syntax highlighting on page as the ... may have resulted in not detecting the end of function.

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-10.0/caller-argument-expression

proposals/csharp-10.0/caller-argument-expression.md

@@ -216,7 +216,7 @@ public static class Debug
         string filePath = callerInfo.FilePath;
         MethodBase method = callerInfo.Method;
         string conditionExpression = callerInfo.ArgumentExpressions[0];
-        ...
+        //...
     }
 }