"KeyError" when pmaports is named something non-standard

@calebccff as mentioned in chat:

  File "/home/luca/dev/postmarketOS/pmbootstrap/pmb/__init__.py", line 71, in main
    return config_init.frontend(args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/luca/dev/postmarketOS/pmbootstrap/pmb/config/init.py", line 694, in frontend
    channel = ask_for_channel(config)
              ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/luca/dev/postmarketOS/pmbootstrap/pmb/config/init.py", line 124, in ask_for_channel
    channels_cfg = pmb.helpers.git.parse_channels_cfg(pkgrepo_default_path())
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/luca/dev/postmarketOS/pmbootstrap/pmb/meta/__init__.py", line 38, in __call__
    self.cache.cache[key] = self.func(*args, **kwargs)
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/luca/dev/postmarketOS/pmbootstrap/pmb/helpers/git.py", line 129, in parse_channels_cfg
    remote = get_upstream_remote(aports)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/luca/dev/postmarketOS/pmbootstrap/pmb/helpers/git.py", line 102, in get_upstream_remote
    urls = pmb.config.git_repos[name_repo]
           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
KeyError: 'aports1'

Relevant pmbootstrap config snippet:

[pmbootstrap]
aports = /home/luca/dev/postmarketOS/aports1

To reproduce just run e.g. pmbootstrap init with pmbootstrap master with aports set to a directory that's not named "pmaports" I guess.