charmcraft publish-lib exits with 0 even if publishing fails

[lucabello]

Bug Description

Currently charmcraft publish-lib correctly fails the library push if something's wrong with LIBPATCH (e.g., LIBPATCH is not bumped, going back, etc). However, the exit of the command is always 0.

This is a problem especially in CI, where a "publish libraries" step will never fail (because of the 0 exit code), and thus is undetectable.

To Reproduce

1. Take a charm library of any charm you own
2. Modify the LIBPATCH to LIBPATCH-1
3. Run charmcraft publish-lib on that library
4. Read the failure message and check the exit code (it will be 0)

Environment

charmcraft 3.2.2.post72+g3a094837 (3.x/edge) (but you can reproduce this with any version)

charmcraft.yaml

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Relevant log output

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