Ensure example error matches the comment

Replace the trailing semicolon with a comma, so that RLS raises an error about "pattern does not mention field `x`" instead of "expected one of `,`, `.`, `?`, `}`, or an operator, found `;`"

Author: sambernard

src/flow_control/match/destructuring/destructure_structures.md

@@ -22,7 +22,7 @@ fn main() {
         // and you can also ignore some variables:
         Foo { y, .. } => println!("y = {}, we don't care about x", y),
         // this will give an error: pattern does not mention field `x`
-        //Foo { y } => println!("y = {}", y);
+        //Foo { y } => println!("y = {}", y),
     }
 }
 ```