fix typo in test

Co-authored-by: Marijn Schouten <[email protected]>

tests/ui/lint/default-groups-issue-65464.rs

@@ -4,7 +4,7 @@
 // explaining lint level and source for builtin lints with default settings.
 //
 // Ideally, we'd like to use lints that are part of `unused` group as shown in the issue.
-// This is not possible in an ui test, because `unused` lints are enabled with `-A unused`
+// This is not possible in a ui test, because `unused` lints are enabled with `-A unused`
 // in such tests, and the we're testing a scenario with no modification to the default settings.
 
 fn main() {