[github action] display black result in job summary

[tieum]

Description

This PR updates the black github action to display the output of black in the job summary

Checklist

• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

Result looks like this:

- erroring with verbosity on

- success with verbosity off

[cooperlees]

Just checking if we should care about the new lines, I feel it might mess up output people maybe parse and make things harder to read ...

[cooperlees]

Do we care about the newline here you've removed? If so I recommend sticking with print cause I believe it will send correct newline in windows ...

Suggested change

	sys.stderr.write("::error::Failed to detect action version.")
	print("::error::Failed to detect action version.", file=sys.stderr, flush=True)

[tieum]

It does need to be written to stderr so as errors do not appear in the job summary part (which won't parse it correctly) but the annotation one, like this:

I've updated the PR with your feedback

[tieum]

I also checked action was correctly running on a Windows runner, an example run is here https://github.com/tieum/atuin-graph/actions/runs/4972553308

[cooperlees]

Thanks for taking my suggestions into account. This all looks good to me now to get the nicer summary and does the right thing to stderr output for all platforms :)