completions: bash template does not handle sub-commands

[abn]

$ poetry --version
Poetry (version 1.2.0b2dev0)
$ echo $BASH_VERSION
5.1.16(1)-release
$ poetry completions bash | bash
bash: line 40: syntax error near unexpected token `clear'
bash: line 40: `            (cache clear)'

Originally reported at https://github.com/python-poetry/poetry/issues/4572.