[lengau]

Purpose

Source-plus-docs filter test, stacked on #630. Not intended
to merge.

This branch changes one source file and one documentation file:

File	Classified as
Makefile	source
docs/README.md	docs

Both are needed in this PR's own diff, because dorny/paths-filter compares
against the PR's base branch. The base is #630's branch, so
the parent's documentation change is not part of this diff.

What it tests

The "yes-docs, yes-code" case. All three linting jobs must start:

Job	Expected	Why
filter	runs	always
files (make -k lint-code)	runs and passes	Makefile is not excluded from source-files
docs (make -k docs-lint)	runs and passes	docs-files matches docs/**
linkcheck (make -k docs-linkcheck)	runs, then fails	docs-files matches docs/**, but this stack has no docs-linkcheck target

The linkcheck failure is the same one #627 already shows.
This PR confirms it is not conditional on the source change, only on the
documentation change.

Related

• ci(lint): improve CI UX when splitting linter jobs #625
• ci: test starbase main with starflow's split lint workflow #627
• docs: add docs-linkcheck to the commands to test #630
• ci(lint-python): split linting into code, docs, and linkcheck jobs starflow#199