chore: Fix several style lints (#17488)

It's not comprehensive enough to start linting on `style` group, but
hey, it's a start.

Release Notes:

- N/A

crates/vim/src/normal/yank.rs

@@ -121,7 +121,7 @@ impl Vim {
                 if is_first {
                     is_first = false;
                 } else {
-                    text.push_str("\n");
+                    text.push('\n');
                 }
                 let initial_len = text.len();
 
@@ -147,7 +147,7 @@ impl Vim {
                     text.push_str(chunk);
                 }
                 if is_last_line {
-                    text.push_str("\n");
+                    text.push('\n');
                 }
                 clipboard_selections.push(ClipboardSelection {
                     len: text.len() - initial_len,