fix: refactor _importCoreModule so required core module is consistent

[jonasongg]

fixes #15077

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• ✅ login: jonasongg / name: jonasongg (851a72c, 0d7ecf5, f530b65)
• ✅ login: SimenB / name: Simen Bekkhus (c71a8c9)

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[SimenB]

Thanks for the PR! Mind adding a test that covers the bug as well?

[jonasongg]

@SimenB Given the original bug's flakiness, is it a good idea to test the private method _importCoreModule? Apologies for my unfamiliarity with the codebase - if you could point me in a general direction to go ahead with the testing?

[SimenB]

I was thinking we could do an integration test where we add a property to a node core module while it's loading, but I think it'd be fiddly as we cache the module, so we'd have to do something in parallel and somehow time it right. Doesn't sound like a stable test at all, so let's ship this as-is 👍