Zig docs builds frequently failed on CI, see #273. Two cases were observed:

1. Zig docs builds failed when remote execution was enabled.
2. Zig docs builds failed locally on MacOS with Zig version 0.12.0.

The first case is addressed by moving Zig docs build tests into a separate CI job and disabling remote execution in that case.
The second case is addressed by marking Zig docs targets as incompatible with Zig version 0.12.0 and MacOS systems.

This is a workaround, not a proper fix of #273.

• Remove test.sh check from CI script
• Tag all Zig documentation targets
• Use tag filters to skip Zig docs builds
• Add separate Zig docs tests
• Exclude zig-docs in presubmit.yml
• build_test target for runfiles docs
• Zig docs tests for all Zig versions using transitions
• Reduce zig-docs CI matrix
• Disable remote execution on Zig docs tests
• Avoid parallelism for Zig docs builds
• Skip Zig docs on MacOS with Zig 0.12.0