other: add test to validate default config, fix typo in default config

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

Adds an additional test to ensure that the default config is valid TOML, as well as actually catch a typo in the default config.

This also adds scaffolding to check if it matches the default config, but currently the way we do that internally is a bit of a hack so I didn't actually enable the assert (as it fails). I'll handle that in another PR as I refactor some things like the internal layout.

Issue

If applicable, what issue does this address?

Closes: #

Testing

If relevant, please state how this was tested. All changes must be tested to work:

If this is a code change, please also indicate which platforms were tested:

• Windows
• macOS
• Linux

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.27%. Comparing base (4c83672) to head (3b969b2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1552      +/-   ##
==========================================
+ Coverage   41.20%   43.27%   +2.07%     
==========================================
  Files         113       99      -14     
  Lines       17808    16962     -846     
==========================================
+ Hits         7338     7341       +3     
+ Misses      10470     9621     -849     

Flag	Coverage Δ
macos-12	?
ubuntu-latest	43.27% <100.00%> (+0.10%)	⬆️
windows-2019	?

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