fix: output non-zero code when devenv test fails

[sandydoo]

Make sure we don't exit with code 0 if devenv test fails.

This requires both a module and a CLI update. On older versions of devenv, the updated tasks runner will cut of a bit of output at the end ("Tests failed :("), as it bails out of the nix develop command early.

I would've preferred something like cmd.run().await?.bail_on_error(), where we can make the decision to bail on each invocation, but that's a bit too invasive at this time.

Reported on Discord.

[sandydoo]

Nice! Caught some test errors.

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View logs

[sandydoo]

Hmmm can't get it to fail locally 🤔

[sandydoo]

✔ Building shell in 0.0s.
/nix/store/s5mr3j8hj6ph3ppx03q46r6jjdldbkfg-init-npm.sh: line 18: /nix/store/230hxd4jaz9rdk20dh66na4bx26c10fc-nodejs-slim-20.11.1/bin/npm: No such file or directory
/nix/store/s5mr3j8hj6ph3ppx03q46r6jjdldbkfg-init-npm.sh: line 18: /nix/store/230hxd4jaz9rdk20dh66na4bx26c10fc-nodejs-slim-20.11.1/bin/npm: No such file or directory

[sandydoo]

Depends on #1511.