[doc][DOC-941] unpin tf-keras: 2.20.0 was yanked

[dstrodtman]

Why

tf-keras==2.20.0 is pinned in doc/requirements-doc.txt and was yanked from PyPI. The RtD build log on #63344 surfaced the warning:

WARNING: The candidate selected for download or install is a yanked version: 'tf-keras' candidate (version 2.20.0 at https://files.pythonhosted.org/packages/50/9b/.../tf_keras-2.20.0-py3-none-any.whl)
Reason for being yanked: <none given>

The warning doesn't fail the build today (fail_on_warning: true doesn't catch yank warnings), but a yanked version may be removed from the index in the future and break the lock.

What

Patch bump to the next non-yanked release:

• doc/requirements-doc.txt: tf-keras==2.20.0 → tf-keras==2.20.1.
• python/deplocks/docs/docbuild_depset_py3.10.lock: update the tf-keras entry with the 2.20.1 wheel and sdist hashes.

2.20.1 has identical requires_dist to 2.20.0 (tensorflow<2.21,>=2.20), so the existing tensorflow==2.20.0 pin still satisfies the constraint and no transitive deps churn. Manual lock edit per the #63130 pattern is appropriate here.

The ML / dl-cpu-requirements.txt / dl-gpu-requirements.txt pins and the doctest_depset lockfile also reference 2.20.0; those are out of scope for this doc-tagged PR and can follow up separately.

Verification

RtD PR preview build with fail_on_warning: true. Confirm the yanked-version warning disappears and no new warnings appear.

Context

Part of the DOC-932 campaign: Ray docs dependency upgrades. Independent of the other open probes (#63343, #63344, #63354) — targets master directly.

DOC-941

[gemini-code-assist]

Code Review

This pull request updates the tf-keras dependency to version 2.20.1 in the documentation requirements and lock file. The reviewer recommends updating all other requirement files referencing the yanked version for consistency and suggests regenerating lock files using standard tools rather than manual edits.

[gemini-code-assist]

While this update addresses the yanked version for the documentation build, the PR description notes that other requirement files (e.g., dl-cpu-requirements.txt, dl-gpu-requirements.txt) and lockfiles still reference tf-keras==2.20.0. To ensure repository-wide consistency and prevent build failures in other components, it is recommended to update all occurrences of the yanked version in this PR rather than following up separately.

[gemini-code-assist]

Manual editing of lock files is generally discouraged as it can lead to inconsistencies in metadata or missed transitive dependency updates. It is safer to regenerate the lock file using the project's standard dependency management tool (e.g., pip-compile) to ensure all hashes and relationships are correctly captured and synchronized.

[dstrodtman]

Both points are addressed in the PR body:

• Scope — Intentional [doc]-tag scoping. The dl-cpu-requirements.txt / dl-gpu-requirements.txt / doctest_depset references are out of scope for a docs-tagged PR and will follow up separately. Bundling would expand the CI surface and reviewer set without changing the fix.
• Manual lock edit — Follows the [doc] add sphinx-llms-txt to generate /llms.txt and /llms-full.txt #63130 pattern (merged), which made the same kind of manual edit to this same lockfile. tf-keras==2.20.1's requires_dist is identical to 2.20.0, so there are no transitive changes for pip-compile to capture.