fix: update @heroku-cli/heroku-exec-util to v0.9.1

[k80bowman]

Needed in order to fix heroku/cli#3147 (final fix will require update to CLI as well).

Testing

• pull down this branch and run yarn
• make sure you are on the latest version of the Heroku CLI (v10.0.0)
• from the root directory for this project, run heroku plugins:link. This will link your local version to the CLI as a plugin.
• using an app with a running dyno, run heroku ps:exec -a APP_NAME
• the connection should succeed
• run heroku plugins:unlink ps-exec to remove the link

[sbosio]

Works as a charm!