Setup testing for nodejs 18

[beardyman]

As a maintainer and user of forge, I want to be able to test on all supported versions of nodejs.

A/C:

• Forge works on nodejs 18
• Tests successfully run using nodejs 18 in CI / GitHub actions

Notes:

• During initial assessment, a large majority of tests fail when running on node 18. Modules aren't being properly mocked via esmock. It looks like node 18 changed the cli argument to specify a module loader (--loader) to --experimental-loader according to the nodejs docs, however a quick test didn't yield successful results.