Replace serde_yaml

[perryqh]

serde_yaml is no longer maintained and we have multiple workarounds for its deficiencies.

Perhaps https://github.com/Ethiraric/yaml-rust2? Is there something else we should consider?

[ivy]

I spent a minute looking for some alternatives:

• serde-yaml-ng - This fork was started in May but maybe @acatton has more context about their plans for this project! 🙏
• yaml-rust2 with serde_yaml2 - This looks slightly more involved than a drop-in replacement.

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Also sharing some links we might revisit later about the sudden discontinuation of serde_yaml and alternatives:

• Reddit thread
• Rust forum thread
• Mastodon thread
• GitHub search: serde_yaml