Infra: errors blocking migration towards docutils 0.22+

Following the work in #4087, I have decided to investigate possible issues with going further, towards docutils 0.22+. The following are extracts from the errors failing the build process (tested on Sphinx 9.1.0 and docutils 0.22.4). I have error logs with full tracebacks and more details available if needed.

Errors

• peps/pep-0554.rst:29: (ERROR/3) Indirect hyperlink target (id="concurrency") refers to target "concurrency", which is a duplicate, and cannot be used as a unique reference.
• peps/pep-0683.rst:476: (ERROR/3) Indirect hyperlink target (id="documentation") refers to target "documentation", which is a duplicate, and cannot be used as a unique reference.
• peps/pep-0426.rst:748: (ERROR/3) Duplicate target name, cannot be used as a unique reference: "extras".
• peps/pep-0653.rst:722: (WARNING/2) Footnote content expected.
• peps/pep-0827.rst:1963: (WARNING/2) Footnote content expected.
• peps/pep-0697.rst:250: (ERROR/3) Indirect hyperlink target (id="reference-implementation") refers to target "reference implementation", which is a duplicate, and cannot be used as a unique reference.
• peps/pep-0791.rst:163: (ERROR/3) Indirect hyperlink target (id="id1") refers to target "motivation", which is a duplicate, and cannot be used as a unique reference.

All of those errors are coming from docutils, not from Sphinx, but they are hard-failing the parallel Sphinx builds.

CC @hugovk

EDIT: After investigation, only docutils is blocked. Sphinx 9 works fine.

Bắt đầu bằng cách tái hiện bản build Sphinx song song với Sphinx 9.1.0 và docutils 0.22.4, sau đó kiểm tra các vị trí được báo cáo trong peps/pep-0554.rst, peps/pep-0683.rst, peps/pep-0426.rst, peps/pep-0653.rst, peps/pep-0827.rst, peps/pep-0697.rst và peps/pep-0791.rst. Công việc được xem là hoàn tất khi các lỗi và cảnh báo docutils được liệt kê không còn khiến bản build bị hard-fail, đồng thời vẫn giữ nguyên nội dung PEP.