macOS CI is failing for 3.13 due to Tcl/Tk 9 on Homebrew

[hugovk]

Bug report

Bug description:

The recent builds on the 3.13 and 3.12 branches are failing for macos-13 (and 3.11 and earlier likely will as well):

• https://github.com/python/cpython/actions/workflows/build.yml?query=branch%3A3.13
• https://github.com/python/cpython/actions/workflows/build.yml?query=branch%3A3.12

For example https://github.com/python/cpython/actions/runs/12052665181/job/33606528979#step:9:1072 :

2 tests failed:
    test_tkinter test_ttk

---

This is because we install unpinned Tcl/Tk from Homebrew which has recently upgraded from 8.6 to 9.0:

cpython/.github/workflows/reusable-macos.yml

Line 40 in 9328db7

run: brew install pkg-config openssl@3.0 xz gdbm tcl-tk make

main isn't failing because it's also recently been updated to prepare for 9.0.

For now, let's pin main and earlier branches to 8.6 and start testing 9.0 later (or on a buildbot):

https://formulae.brew.sh/formula/tcl-tk@8

CPython versions tested on:

3.12, 3.13, 3.14

Operating systems tested on:

macOS

Linked PRs

• gh-127359: Pin Tcl/Tk to 8 (8.6) for testing macOS #127365
• [3.13] gh-127359: Pin Tcl/Tk to 8 (8.6) for testing macOS (#127365) #127393
• [3.12] gh-127359: Pin Tcl/Tk to 8 (8.6) for testing macOS (GH-127365) #127394
• [3.11] gh-127359: Pin Tcl/Tk to 8 (8.6) for testing macOS (GH-127365) #127407
• [3.10] gh-127359: Pin Tcl/Tk to 8 (8.6) for testing macOS (GH-127365) #127408
• [3.9] gh-127359: Pin Tcl/Tk to 8 (8.6) for testing macOS (GH-127365) #127409

[hugovk]

I'll open backports for security branches too, at least 3.11 is failing (and very likely 3.9-3.10 too).

https://github.com/python/cpython/actions/runs/12084805591