Trigger unified-docs deployment on every push to main

[samuelcolvin]

The unified-docs library config for httpx2 pins its source to the main branch, so any rebuild of the unified site already pulls httpx2 docs from main. Dispatching only on tag pushes meant a release deployed docs at the tag SHA, and the next unrelated rebuild of the site would pull newer main content anyway. Logfire already dispatches on every push to main for the same reason.

This moves the deploy-docs job from publish.yml to main.yml. It depends on the check job and runs only when success() && github.ref == 'refs/heads/main', so pull requests and failed test runs skip it. The dispatch payload still pins the exact commit SHA.

[codspeed-hq]

Merging this PR will not alter performance

✅ 17 untouched benchmarks
⏩ 7 skipped benchmarks¹

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_{Comparing deploy-docs-on-main (2e908f6) with main (32c40d9)}

Footnotes

1. 7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}