Split docs build and publish

[martincostello]

Separate the build and publish process for the documentation into two jobs so the concurrency only applies to publishing.

This should stop PRs being opened around the same time as each other (e.g. dependabot) having the docs jobs cancelled by GitHub.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.67%. Comparing base (9084bb0) to head (8e2a99a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2054   +/-   ##
=======================================
  Coverage   83.67%   83.67%           
=======================================
  Files         312      312           
  Lines        7105     7105           
  Branches     1054     1054           
=======================================
  Hits         5945     5945           
  Misses        789      789           
  Partials      371      371           

Flag	Coverage Δ
linux	?
macos	?
windows	83.67% <ø> (ø)

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