ci: migrate deprecating set-output commands

[miles170]

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Closes #2144.

Description of the changes being introduced by the pull request:

Replace deprecating set-output command with $GITHUB_OUTPUT.

Please verify and check that the pull request fulfills the following
requirements:

• The code follows the Code Style Guidelines
• Tests have been added for the bug fix or new feature
• Docs have been added for the bug fix or new feature

[coveralls]

Pull Request Test Coverage Report for Build 3310900583

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 98.104%

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Totals
Change from base Build 3297205557:	0.0%
Covered Lines:	1346
Relevant Lines:	1362

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💛 - Coveralls

[jku]

this looks good to me.

I can't run an action from a branch in your repo but I'm also not going to make you setup actions on your repo just for this: I'll merge this, run the action manually to verify, and will comment here to document the results...

[jku]

✔️ https://github.com/theupdateframework/python-tuf/actions/runs/3311880108:

The latest TUF specification version (v1.0.31) matches with the version that theupdateframework/python-tuf supports (v1.0.31)

Thanks @miles170