[FEATURE] Use warnings/errors for CI builds.

[vintagepc]

Is your feature request related to a problem? Please describe.
CI builds can issue warnings/errors with filenames and line numbers - make use of that fir things like code lint as it makes a nice annotation on the action result rather than needing to trawl through the logs.

https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-commands-for-github-actions#setting-a-warning-message

::error file={name},line={line},col={col}::{message}

and
::warning file={name},line={line},col={col}::{message}

[vintagepc]

Ooooh, this is very nice!

And it even inlines it if the issue is on a changed line: