GHA: Replace deprecated set-output

[dweindl]

see https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

[codecov-commenter]

Codecov Report

Merging #186 (d4b94b7) into develop (8e2ad79) will decrease coverage by 0.07%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #186      +/-   ##
===========================================
- Coverage    78.55%   78.48%   -0.08%     
===========================================
  Files           29       29              
  Lines         2742     2742              
  Branches       659      604      -55     
===========================================
- Hits          2154     2152       -2     
- Misses         427      428       +1     
- Partials       161      162       +1     

Impacted Files	Coverage Δ
petab/lint.py	74.77% <0.00%> (-0.61%)	⬇️

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