Fix CI failures caused by docs build memory exhaustion

[pankajkoti]

The Sphinx docs build had outgrown the memory available on
pre-commit.ci runners and was failing consistently on every pull
request, including ones that touched no documentation at all. The
result was a red pre-commit.ci check on unrelated PRs, blocked merges,
time lost to investigating failures that had nothing to do with the
change under review, and an erosion of trust in required checks.

Running the docs build on GitHub Actions restores that trust. PRs
that do not touch docs or library sources now pass cleanly. PRs that
do touch them get a reliable pass/fail signal with enough memory to
actually complete the build, so warnings surface where they belong
rather than being masked by OOM failures. pre-commit.ci is left to
focus on what it is good at, fast lint and format checks, and
reviewers and contributors get back the signal they rely on to ship
changes confidently.

related: #2578
related: #2579

[pankajkoti]

Successful docs build GitHub actions run triggered from this branch: https://github.com/astronomer/astronomer-cosmos/actions/runs/24655247815/job/72087052273?pr=2580#step:5:331

Successful pre-commit.ci run from this PR: https://results.pre-commit.ci/run/github/577757880/1776672058.2nwJK3-bTuiR4xYgq_mZqA

[Copilot]

Pull request overview

Moves the Sphinx docs build out of pre-commit.ci (where it was OOM’ing) into a dedicated GitHub Actions workflow so docs builds run with adequate resources and only when docs/library sources change.

Changes:

• Remove the local check-docs-build hook from .pre-commit-config.yaml.
• Add a new .github/workflows/docs-build.yml workflow to install docs deps and run sphinx-build.
• Update .github/workflows/test.yml changed-files filter to treat docs-build.yml as non-code (so it won’t trigger full test runs by itself).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
.pre-commit-config.yaml	Removes the Sphinx build hook that was exhausting memory on pre-commit.ci.
.github/workflows/test.yml	Ensures edits to the new docs-build workflow don’t force the full test matrix to run.
.github/workflows/docs-build.yml	Introduces a dedicated CI docs build job for PRs/changes impacting docs or cosmos/.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.05%. Comparing base (37fd06c) to head (c3d9af7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2580   +/-   ##
=======================================
  Coverage   98.05%   98.05%           
=======================================
  Files         103      103           
  Lines        7601     7601           
=======================================
  Hits         7453     7453           
  Misses        148      148           

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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[tatiana]

Thanks for fixing this, @pankajkoti !