[tests] Address regularly failing Windows test "tcl"

[ourownstory]

---------- coverage: platform win32, python 3.10.11-final-0 ----------
Coverage XML written to file coverage.xml

=========================== short test summary info ===========================
FAILED tests\test_plotting.py::test_plot_conformal_prediction_asymmetric[matplotlib] - _tkinter.TclError: Can't find a usable init.tcl in the following directories:
{C:\hostedtoolcache\windows\Python\3.10.11\x64\tcl\tcl8.6}

C:/hostedtoolcache/windows/Python/3.10.11/x64/tcl/tcl8.6/init.tcl: couldn't read file "C:/hostedtoolcache/windows/Python/3.10.11/x64/tcl/tcl8.6/init.tcl": No error
couldn't read file "C:/hostedtoolcache/windows/Python/3.10.11/x64/tcl/tcl8.6/init.tcl": No error
while executing
"source C:/hostedtoolcache/windows/Python/3.10.11/x64/tcl/tcl8.6/init.tcl"
("uplevel" body line 1)
invoked from within
"uplevel #0 [list source $tclfile]"

This probably means that Tcl wasn't installed properly.
=========== 1 failed, 132 passed, 380 warnings in 747.06s (0:12:27) ===========

[ourownstory]

Likely connected to plots opening during tests.

[SimonWittner]

Should be fixed with #1445.