Add back macos to test matrix

[kinow]

These changes close #590

We've updated to yarn v3. I think macos build should work fine now? It passed on my fork's GH actions. I'll retrigger it a couple times now to confirm it's working OK.

Requirements check-list

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Already covered by existing tests.
• No change log entry required (why? e.g. invisible to users).
• No documentation update required.

[codecov-commenter]

Codecov Report

Merging #713 (f31c442) into master (8547b6f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #713   +/-   ##
=======================================
  Coverage   89.97%   89.97%           
=======================================
  Files          79       79           
  Lines        1536     1536           
  Branches      113      113           
=======================================
  Hits         1382     1382           
  Misses        122      122           
  Partials       32       32           

Flag	Coverage Δ
e2e	77.99% <ø> (ø)
unittests	79.90% <ø> (ø)

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[kinow]

Triggered new jobs, no issues found. Should be good to be reviewed & merged 🤞