[wildcards] don’t overreport `parameter_assignments`

Fixes: https://github.com/dart-lang/linter/issues/5041

Change-Id: I128933b8f5c720acbbc2ec57a90dc2992977bb05
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/378571
Commit-Queue: Phil Quitslund <pquitslund@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/linter/test/rules/parameter_assignments_test.dart

diff --git a/pkg/linter/test/rules/parameter_assignments_test.dart b/pkg/linter/test/rules/parameter_assignments_test.dart
index c6a7a15..94889c8 100644
--- a/pkg/linter/test/rules/parameter_assignments_test.dart
+++ b/pkg/linter/test/rules/parameter_assignments_test.dart
@@ -39,6 +39,17 @@
     ]);
   }
 
+  test_assignment_wildcard() async {
+    await assertDiagnostics(r'''
+void f([int? _]) {
+  _ = 8;
+}
+''', [
+      // No lint.
+      error(CompileTimeErrorCode.UNDEFINED_IDENTIFIER, 21, 1),
+    ]);
+  }
+
   @FailingTest(reason: 'Closures not implemented')
   test_closure_assignment() async {
     await assertDiagnostics(r'''