GHA: add workflow to require changelog label

[hugovk]

For #3.

Changes proposed in this pull request:

• This requires one of the "changelog: X" labels to be added
• Those labels are used by release drafter to draft the release, and also figure out the next release number
• And we can add it make it a required check too so it's not forgotten

[codecov-commenter]

Codecov Report

Merging #10 (76a8fef) into main (d3759d5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #10   +/-   ##
=======================================
  Coverage   99.68%   99.68%           
=======================================
  Files           9        9           
  Lines         635      635           
=======================================
  Hits          633      633           
  Misses          2        2           

Flag	Coverage Δ
GHA_Ubuntu	98.42% <ø> (ø)
GHA_Windows	98.11% <ø> (ø)
GHA_macOS	98.42% <ø> (ø)

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