Abort upgrade if config won't serialize instead of running default configuration

[focusaurus]

What did you expect to happen?

When running topgrade with an unfield in the configuration, I expect topgrade to abort with an error exit code and clear error message including the full path to the config file and a clear error message.

What actually happened?

topgrade proceeded with a default config and upgraded many things I usually disable upgrades for.

Additional Details

• Which operating system or Linux distribution are you using? arch linux
• How did you install Topgrade? AUR I think
• Which version are you running? Topgrade 9.0.1

2022-07-24T14:59:55.643Z ERROR topgrade::config > failed to load configuration: unknown field `pamac_arguments`, expected one of `yay_arguments`, `arch_package_manager`, `show_arch_news`, `trizen_arguments`, `pikaur_arguments`, `dnf_arguments`, `apt_arguments`, `enable_tlmgr`, `redhat_distro_sync`, `rpm_ostree`, `emerge_sync_flags`, `emerge_update_flags` for key `linux` at line 18 column 1