Drop support for Python 3.8 (April 2025)

[srittau]

Python 3.8 has reached its end-of-life phase on 2024-10-07 (PEP 569).

How to remove support

January 2025

• Update the documentation. (Officially drop Python 3.8 support #13386)
• Update the oldest_supported_python key in pyproject.toml. (Officially drop Python 3.8 support #13386)
• Remove requires_python >= 3.9 and python_version >= 3.9 from METADATA.toml (Officially drop Python 3.8 support #13386)
• Remove 3.8 from CI and test scripts. (Remove Python 3.8 from CI #13387)
• Update stubtest allow lists. Also check whether items can be moved to the common allow lists. (Remove Python3.8 stubtest allowlists #13389)

April 2025

• Remove 3.8 exclusive branches from stubs. (Drop Python 3.8 branches #13776)
• Remove obsolete stdlib modules (see VERSIONS). (Remove dummy threading modules #13771)
  • _dummy_thread
  • _dummy_threading
  • dummy_threading
• Replace typing_extensions imports: no op for Python 3.8 -> 3.9
• Remove backports.zoneinfo from EXTERNAL_REQ_ALLOWLIST in stub_uploader.metadata (Remove backports.zoneinfo for ext req allowlist typeshed-internal/stub_uploader#168)

(Please amend as necessary.)

[AlexWaygood]

I think a lot of the "remove redundant version branches" work would be done automatially with we a Ruff autofix if we bumped this:

typeshed/pyproject.toml

Line 21 in ad8ecaf

target-version = "py38"

[srittau]

I've nearly finished with removing the branches. It's honestly not that difficult and you catch a few things when doing it manually.

[AlexWaygood]

oh, I don't object, just thought it might save a bit of work :-) doing it manually is fine, of course!

[srittau]

It's also quite relaxing work. PLEASE DON'T TAKE IT FROM ME!!!!!

[brianschubert]

slowly closes open PR tab