Ignore unused parameters in snippet code (#131068)

Add `unused_element_parameter` to the codes ignored while analyzing snippets.

Fixes https://github.com/flutter/flutter/issues/131067

dev/bots/analyze_snippet_code.dart

@@ -459,6 +459,7 @@ class _SnippetChecker {
     '// ignore_for_file: unnecessary_import',
     '// ignore_for_file: unreachable_from_main',
     '// ignore_for_file: unused_element',
+    '// ignore_for_file: unused_element_parameter',
     '// ignore_for_file: unused_local_variable',
   ];