docs: retire the counted numbers that tests and the python-versions updater pin (#1811)

[JarryShaw]

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• Followed the coding style (make pylint, make mypy, make isort)

• make test passes, and a test case covers the change. Narrow runs only, listed below.

• Added a changelog entry under docs/source/changelog/ and regenerated CHANGELOG.md, if the change is user-visible: N/A — centralised in docs(changelog): shared 1.5.0 changelog — long-lived, merges last (#610, #616, #617, #618, #620) #657

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Summary

Applies the ruling on #1103 (no counted numbers in the docs) to the pages whose counts tests and the python-versions updater pinned. The prose and its pins go in one change.

• Prose: process.rst, registry-protocol.rst, sentinel-convention.rst, workflows.rst and releasing.rst lose their pinned counts and the sentences that quoted them. Each rewrite was checked against the tree.

• Pins: each is deleted, or replaced by a check of the underlying fact without a number in prose:

  • changelog sections must be exactly one per package plus Project infrastructure;
  • the sentinel table must match the module's singletons both ways;
  • every workflow file needs a row and a graph node;
  • the gate-only list must equal unit-tests.yml's gated matrix jobs;
  • the hand-kept experimental legs must be experimental.yml's.

  Every replacement guard fails when its fact breaks.

• Updater (util/): the claims that rewrote counts are gone, and every version-range and latest-version claim stays. No workflow YAML changes.

• Runs: tests/project and the sentinel test pass, and the changed modules pass under plain unittest too.

Unpinned counts on these pages are left for #1103's round 3.

Closes #1811

[JarryShaw]

Verdict: GOOD TO GO at 197bf1952. A Sonnet cross-review (author: Opus) checked each rewritten sentence against the tree: the gated jobs in unit-tests.yml, experimental.yml's matrix, a runtime walk of the enumerations, and the changelog sections. It found no remaining pin that matches a number in prose. Each replacement guard fails when its fact breaks. The updater still rewrites versions, and no workflow YAML changed. tests/project passes, and the changed modules pass under plain unittest. No file of another open PR is touched.