* make build.yml reproducible
`build.yml` is currently biased to succeed every time on this repository. Reasoning is that it will always checkout the actions' repository (which essentially transfers the actions' files to the "working directory", not the case if this action is being used externally), and it assumes that the action is run locally.
This commit breaks the build file into two parts: one that performs the current action as-is, and a new job which attempts to simulate usage from an external repository. In this job, no initial checkout is made and an immediate attempt at connecting to a ZeroTier network is made.
* trigger workflow run
* build.yml: only run test job on main
This forces the `test` job to only run if the workflow was triggered from the `main` branch. It wouldn't make sense to check if `main` works when using a different branch or tag, so this avoids doing that entirely.
`test` cannot automatically use the ref that triggered this workflow because `uses` does not take in expressions (and therefore cannot use `github.ref_name`).
* action.yml: force use external syntax for `uses`
This forces the use of the syntax for `uses` calling a specified subfolder of a public repository at a given ref. This is an attempt at moving away from the use of `./` as a path, which forces GitHub Actions to locate the `util/post/action.yml` of the *working directory* and not of the action path. This exists since `uses` cannot take expressions; this would be an easy fix if `./` can be replaced with `${{ github.action_path }}/`. Alas, this is not possible, and this hacky workaround exists instead.
* action.yml: use `action_path` instead of `./`
This replaces the use of `./` with `${{ github.action_path }}`, to allow the install scripts to run outside the action's repository, see b1b5340 for related commit.
* action.yml: wrap pwsh argument in quotes