fix: universal2 tags computation was incorrect

[henryiii]

Was based on the wrong assumption for ARCHFLAGS.

[codecov]

Codecov Report

Merging #97 (09a62d4) into main (a163308) will decrease coverage by 0.03%.
The diff coverage is 87.50%.

❗ Current head 09a62d4 differs from pull request most recent head f13a23a. Consider uploading reports for the commit f13a23a to get more accurate results

@@            Coverage Diff             @@
##             main      #97      +/-   ##
==========================================
- Coverage   90.95%   90.91%   -0.04%     
==========================================
  Files          44       44              
  Lines        1702     1707       +5     
==========================================
+ Hits         1548     1552       +4     
- Misses        154      155       +1     

Impacted Files	Coverage Δ
src/scikit_build_core/builder/builder.py	86.86% <85.71%> (-0.37%)	⬇️
src/scikit_build_core/pyproject/wheel.py	92.59% <100.00%> (ø)

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