ci: bump contributors-png workflow to Node 22

[Vaivaswat2244]

contributors-png.yml was the only workflow still on node-version: 20 —
missed when #8852 moved the rest to 22. Node 20 reached EOL in April, so this
brings it in line.

Kept at 22 to match every other workflow on main rather than jumping to 24,
since the step below runs npm install canvas (a native module) and whether
main moves to 24 is a separate call.

Verified on my fork: npm install canvas and node utils/contributors-png.js
run cleanly on Node 22.

[p5-bot]

Continuous Release

CDN link

• https://raw.esm.sh/pr/p5@bd489b5/lib/p5.min.js

Published Packages

• https://pkg.pr.new/p5@bd489b5

Commit hash: f6d391b

Previous deployments

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This is an automated message.

[limzykenneth]

This is fine and I would actually say go with node 24 if desired. The main CI tasks will be upgraded to node 24 once the dependencies stuff are done anyway. However, there are too many parallel things going on at the moment with the CI tasks, I would like them to be more centralized or it can be hard to keep track of things and we need to solve merge conflicts too often. @ksen0