Clear dirty `schema_cache` after `dump_schema_cache`

`dump_schema_cache` fills `schema_cache` even if the test that modifies
the schema has properly cleared the schema cache.

Fixes #31463.

activerecord/test/cases/tasks/database_tasks_test.rb

@@ -110,6 +110,7 @@ def test_dump_schema_cache
       ActiveRecord::Tasks::DatabaseTasks.dump_schema_cache(ActiveRecord::Base.connection, path)
       assert File.file?(path)
     ensure
+      ActiveRecord::Base.clear_cache!
       FileUtils.rm_rf(path)
     end
   end