`asdf install` should exit with exit code of 0 when a tool version is set to uninstallable system version

asdf install still returns a non-zero exit code with postgres system in my ~/.tool-versions. I'd think it should only exit with a non-zero exit code when trying to install a system version directly, e.g.: asdf install postgres system as in this test case:

https://github.com/asdf-vm/asdf/blob/5646b389f73b31fcb5b10711a0ee06bea4fc6141/test/install_command.bats#L220-L225

I think asdf install should skip over them and return success.

Currently:

复制

➜ asdf install
[...]
skipping uninstallable version system of postgres
version [...] of ruby is already installed
[...]

➜ echo $?                     
1

➜ asdf install postgres system
error installing version: uninstallable version system of postgres

➜ echo $?                     
1

Originally posted by @ZimbiX in #1930