Use default export of jest-environment if present

[noseworthy]

Jest v28 is going to start using ESM, and the latest release candidate
has started exporting modules with ESM syntax:

jestjs/jest#12340

This breaks jest-mongodb when importing jest-environment-node. In order
to properly import this module when running in jest v28 we need to look
for the default export.

If the default export is present, use that, otherwise use the test
environment as normal.

[noseworthy]

Hey @vladgolubev, thanks for your work on this package! It's been super useful to us. We're upgrading to the v28 release candidate of jest in order to take advantage of the new test sharding feature: jestjs/jest#12546

We've got everything else working, but this package is preventing us from upgrading because of how it imports the test environment. I've got a little patch here that works for us and I hope would be backwards compatible for your purposes. I'd really appreciate it if you could take a look when you get a chance.

Thanks!

[vladholubiev]

@noseworthy see https://github.com/shelfio/jest-mongodb/releases/tag/v2.2.1

Thanks for your contribution!

[noseworthy]

Woah, that was super fast. Thanks so much!