fix(asset): reenable on macOS

[dbolduc]

Part of #8145

We require protobuf >= 21.1, which handles TRUE and FALSE macros: https://github.com/protocolbuffers/protobuf/blob/7062d0a2d0075d5e7d5c294fd3984df67a976da3/src/google/protobuf/port_def.inc#L861-L864

We leave the bazel windows build disabled. There is a comment in the linked issue about what breaks.

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[codecov]

Codecov Report

Merging #9468 (0280216) into main (76a4024) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #9468      +/-   ##
==========================================
- Coverage   94.63%   94.63%   -0.01%     
==========================================
  Files        1489     1489              
  Lines      137195   137195              
==========================================
- Hits       129838   129835       -3     
- Misses       7357     7360       +3     

Impacted Files	Coverage Δ
...ud/spanner/integration_tests/client_stress_test.cc	85.52% <0.00%> (-0.66%)	⬇️
...cloud/pubsub/internal/subscription_session_test.cc	97.82% <0.00%> (-0.17%)	⬇️
google/cloud/pubsub/samples/samples.cc	92.35% <0.00%> (-0.08%)	⬇️

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