Bumps Yarn to 1.15

[arcanis]

Summary

This diff uses the yarn-path configuration settings to ensure that Jest always run with the specified Yarn release, regardless of the one used in the global environment.

I've also removed workspaces-experimental since it's not required anymore.

Test plan

Ran yarn -v in the repo, got 1.15. CI should print it as well.

[arcanis]

Node 6 seems to have failed due to an OOM - does that happen regularly?

[jeysal]

Never seen it happen so far, although we do know that tsc -b is terribly slow for us. If it's flaky it must be super rare. No idea how to reproduce this though :/

[jeysal]

Although the tsc process peaks at more than 1.5G RES for me when using Node 6, while it never even hits 500M on current. But I can't really imagine the Yarn version could be involved in this.

[arcanis]

Wow that's a lot! Ok, good to merge then?

[jeysal]

Should do a rerun to be safe. I don't have permission to trigger builds (maybe you do as an org member), otherwise git commit --amend --no-edit and force push :)

[jeysal]

Failed again, this time due to timeout. This hasn't happened on any of the recent master builds. There's something fishy going on here that deteriorates the performance of postinstall yarn build.
Any ideas? Does Yarn mess with the spawned node process in any way since v14/15?

[arcanis]

Nope 🤔 and I don't see memory differences when trying locally with time -v ...

[arcanis]

I may have an idea - my theory is that TypeScript tries to somehow parse the Yarn release file. Since it's relatively large, it crashes on Node 6. I've tried adding those files to the exclude list, let's see what happens.

[jeysal]

Thought about that as well, but allowJs is not enable 🤔

[arcanis]

Seems to have worked! I'll remove the useless releases still checked-in, and if both run are green I'd be relatively confident the problem is fixed. Very interesting to know!

[SimenB]

Oh, that's interesting! It makes sense to ignore it anyways, but it shouldn't die anyways...

[jeysal]

LGTM if CI passes

[SimenB]

The TS step went through, so looking good 🙂

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