Felix, are these still the exact errors you're experiencing? Both in my normal Arch install and in a chroot environment I get the following errors instead:

======================================================================
FAIL: test_winfo_rgb (tkinter.test.test_tkinter.test_misc.MiscTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/cpython/Lib/tkinter/test/test_tkinter/test_misc.py", line 213, in test_winfo_rgb
    self.assertEqual(rgb('#4a3c8c'), (0x4a4a, 0x3c3c, 0x8c8c))
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: Tuples differ: (19016, 15399, 35985) != (19018, 15420, 35980)

First differing element 0:
19016
19018

- (19016, 15399, 35985)
?      ^    ^^^      ^

+ (19018, 15420, 35980)
?      ^    ^^^      ^


======================================================================
FAIL: test_configure_type (tkinter.test.test_tkinter.test_widgets.MenuTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/cpython/Lib/tkinter/test/test_tkinter/test_widgets.py", line 1244, in test_configure_type
    self.checkEnumParam(widget, 'type',
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/cpython/Lib/tkinter/test/widget_tests.py", line 151, in checkEnumParam
    self.checkInvalidParam(widget, name, '',
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/cpython/Lib/tkinter/test/widget_tests.py", line 73, in checkInvalidParam
    with self.assertRaises(tkinter.TclError) as cm:
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: TclError not raised

----------------------------------------------------------------------


In case I'm doing something stupid, here are the commands I used to set-up the chroot environment:

$ CHROOT=chroot
$ mkdir $CHROOT
$ mkarchroot $CHROOT/root base-devel tk git gnu-free-fonts
$ xhost + local:
$ sudo mount --bind $CHROOT/root $CHROOT/root
$ sudo arch-chroot $CHROOT/root
> git clone https://github.com/python/cpython.git
> cd cpython
> ./configure && make -j24
> ./python -m test -v -u gui test_tk

I'll start looking into these errors, since I'm able to reproduce them.