uv step: checking self subcommand exits; fixes #942

[lucaspar]

What does this PR do

Standards checklist

• [x] The PR title is descriptive
• [x] I have read CONTRIBUTING.md
• [x] Optional: I have tested the code myself
• [x] If this PR introduces new user-facing messages they are translated

[SteveLauC]

No need to worry about the i18n CI, you can ignore it:)