Make yarn installs immutable

[kylorhall-atlassian]

What is this change?

Context: https://github.com/atlassian-labs/compiled/pull/1732/files#r1813527167, I've noticed a few times I get yarn.lock diffs staged when they should probably be committed.

Why are we making this change?

To make sure we don't leave out important changes.

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PR checklist

Don't delete me! 🤣

• Testing…this should fail without yarn.lock changes as master is currently broken.

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[kylorhall-atlassian]

Only concern with having this in all the files is the devex could be a bit annoying, but CI runs very quickly here…so I expect it's not worth intentionally omitting it from other workflows.

[kylorhall-atlassian]

Nevermind, I'm confused a bit—this doesn't even seem to work in full like I expected; in Yarn v2+ this works, and then scripts/postinstall.sh confuses me too…I think it's a good idea, but I forget how to execute it. I'll ignore for now.