[WIP] Fix CI and drop support for Node 12

[mikrostew]

Fix CI for this repo, which has been failing for the last few months.

Updated Node LTS Versions

This drops support for Node 12.x (which is EOL as of 2022/04/30).

The tests now run against 14.x and 16.x.

I had to update workerpool to pull in the fix for Node16 mentioned in this issue.

And I updated to a more recent version of Yarn.

Legacy Mocha Tests

These have been failing for a while, with this error:

Error: Unable to require module 'crypto' because it was not in the whitelist.

So I added that to fastbootDependencies, which fixed the issue.

Running with Node 16 surfaced a new error with starting the server in the tests, so I removed the skipNpm: true option to fix that.

Ember-Try Tests

These have also been failing for a while, with this error:

Build Error (broccoli-persistent-filter:Babel > [Babel: @ember/test-helpers]) in @ember/test-helpers/-internal/build-registry.js

[BABEL]: Cannot find module 'babel-plugin-dynamic-import-node/utils'

I fixed that by preventing ember-try from running with --no-lockfile (which it does by default, and was causing a dependency mismatch when running the tests).