ci: add macos to test matrix

[dnalborczyk]

No description provided.

[codecov]

Codecov Report

Merging #675 (89a8c35) into main (c09ace1) will increase coverage by 0.11%.
The diff coverage is 96.77%.

@@            Coverage Diff             @@
##             main     #675      +/-   ##
==========================================
+ Coverage   93.52%   93.64%   +0.11%     
==========================================
  Files          11       12       +1     
  Lines         510      535      +25     
  Branches      183      191       +8     
==========================================
+ Hits          477      501      +24     
- Misses         32       33       +1     
  Partials        1        1              

Impacted Files	Coverage Δ
src/load.ts	91.91% <87.50%> (-0.56%)	⬇️
src/transform/schema.ts	97.97% <100.00%> (+0.38%)	⬆️
src/utils.ts	94.82% <100.00%> (+0.09%)	⬆️
tests/test-utils.ts	100.00% <100.00%> (ø)

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