Improve how this Action's own logs work

[ericcornelissen]

Summary

Improve the ad hoc logging implemented here

tool-versions-update-action/bin/update.sh

Lines 7 to 13 in 9c487be

	info() {
	echo "[info ] $1"
	}
	debug() {
	echo "[debug] $1"
	}

with logging that follows the GitHub Actions logging style (see e.g. @actions/core) so that, for example, debug logs are only shown when enabled.

[ericcornelissen]

Based on the @actions/core implementation ([1], [2], [3]) it looks like logging formatting for GitHub Actions should be done as:

::debug::the debug message
::warning::the warning message
::error::the error message
::notice::the message

with the exception of informational logging ([4]), which is just:

the message