Add `.github/workflows` path to `require` paths

The issue does not name a file or test. Start by locating the require-path setup used by workflow scripts and compare the existing behavior with process.env.NODE_PATH and module.paths. Done means require can search .github/workflows without changing the current project-root behavior.

Is your feature request related to a problem? Please describe.
It took me a while to figure out how to include files in this project, because I had (incorrectly) assumed the relative path was to the .github/workflows folder and not the project root. I would assume this is a common misunderstanding, as the user is writing their script inside that folder.

Describe the solution you'd like
I certainly don't recommend changing the behavior, but simply adding the workflow's .github/workflows path in the list of paths for require to search.

Describe alternatives you've considered
Alternatively, make a way for users to add their own relative paths to the configuration or the script, which might be a better approach.

It seems of the two common ways of doing this (namely, modifying the process.env.NODE_PATH environment variable or pushing a path onto module.paths), neither is implemented. The easiest method might be to simply make use of the process.env.NODE_PATH environment variable as the core functionality does.

Additional context
N/A