Address feedback, fix linter warnings and add CI workflow

[virtualroot]

I have run these linters and fixed their warnings:

• awesome-lint - The awesome list linter.
• markdownlint-cli2 - A Markdown linter.
• lychee - Finds broken URLs inside Markdown.

I added a GitHub workflow to run all the above linters on future pull requests.

I'm also addressing some feedback from https://github.com/sindresorhus/awesome/pull/2895.

I hope these changes help with the awesome-list submission.

[benallfree]

@virtualroot Should I merge and ask for another review in the upstream PR?

[virtualroot]

@benallfree Let's give it a try! :crossed_fingers: