Exclude node_modules from test-tsconfig.json

[zFernand0]

This same issue may apply to other plugins as well.
Solution:

• Remove fs-extra from the __tests__/__src__/environment/TestEnvironment.ts

Downgraded @types/fs-extra for various reasons:

• the test-tsconfig.json cannot properly exclude the @types/fs-extra package since the TestEnvironment.ts uses if for mkdirpSync
• tsconfig.json has to include it's node_modules/typings. See https://stackoverflow.com/a/67512016/16555983
• @types/fs-extra@^9.0.5 has issues that we may be able to avoid with
  tsconfig.json#compilerOptions.skipLibCheck: true

Note: We may have to upgrade to newer versions of this package for security reasons.

Originally posted by @zFernand0 in #85 (comment)