Improve collapsible_match error message syntax

clippy_lints/src/matches/collapsible_match.rs

@@ -96,7 +96,7 @@ fn check_arm<'tcx>(
         // collapsing patterns need an explicit field name in struct pattern matching
         // ex: Struct {x: Some(1)}
         let replace_msg = if is_innermost_parent_pat_struct {
-            format!(", prefixed by {}:", snippet(cx, binding_span, "their field name"))
+            format!(", prefixed by `{}`:", snippet(cx, binding_span, "their field name"))
         } else {
             String::new()
         };