fix: destroy request object after successful response (issue #1489)

[nduthoit]

Checklist

• I have read the documentation.
• I have included a pull request description of my changes.
• I have included some tests.
• (n/a) If it's a new feature, I have included documentation updates in both the README and the types.

Based on my testing this fixes #1489 for v11: late ECONNRESET errors no longer causes the "onCancel handler was attached after the promise settled" error. (I used this gist for testing).

It mimics what is done in v12 by calling request.destroy() after a successful response right before the promise is resolved.

I tried to add a test case where the server would reset the TCP connection and cause an ECONNRESET error after sending a success response but that proved to be challenging to do using an Express server. I also tried using a Python server executed from the test case but it proved to be too brittle to be a good test case. Therefore I landed on a simpler test case that ensures that the request has been destroyed once the promise has successfully resolved.

[sindresorhus]

@nduthoit Looks like the v11 branch no longer builds. So you need to fix the build issues if you want us to do a release.

[sindresorhus]

https://github.com/sindresorhus/got/releases/tag/v11.8.6