Fix an error for rake prof:slow_cops

This commit fixes the following error for `rake prof:slow_cops`
when tmp/stackprof.dump does not exist.

```console
% bundle exec rake prof:slow_cops
rake aborted!
Don't know how to build task 'run' (See the list of available tasks with `rake --tasks`)
tasks/prof.rake:22:in `block (2 levels) in <top (required)>'
/Users/koic/.rbenv/versions/3.2.0-dev/bin/bundle:25:in `load'
/Users/koic/.rbenv/versions/3.2.0-dev/bin/bundle:25:in `<main>'
Tasks: TOP => prof:slow_cops => prof:run_if_needed
(See full trace by running task with --trace)
```

tasks/prof.rake

@@ -19,7 +19,7 @@ namespace :prof do
 
   desc 'Run RuboCop on itself only if dump does not exist'
   task :run_if_needed, [:path] do
-    Rake::Task[:run].run unless File.exist?(dump_path)
+    Rake::Task['prof:run'].invoke unless File.exist?(dump_path)
   end
 
   desc 'List the slowest cops'