[3.9] gh-97032: Set tkinter path for macOS CI

[corona10]

• Issue: GUI tests: CPython 3.9 CI failure for macOS: macOS 11 (1107) or later required, have instead 11 (1106) ! #97032

[corona10]

AS-IS

tkinter.TCL_VERSION: 8.5
tkinter.TK_VERSION: 8.5
tkinter.info_patchlevel: 8.5.9

TO-BE

tkinter.TCL_VERSION: 8.6
tkinter.TK_VERSION: 8.6
tkinter.info_patchlevel: 8.6.12

[ned-deily]

LGTM, thanks!

[ned-deily]

I'm merging this now to unblock 3.9 CI testing for other PRs.