Re-enabled "close window" option on modal dialogs

[rozyczko]

Description

Option WindowContextHelpButtonHint seems to have disabled the "close window" cross icon in PySide6.
The original reason for it was, as the name suggests, the removal of the question mark icon, which by default was set.

Fixes #2688

How Has This Been Tested?

GH Windows installer on Win10 and Win11.

Review Checklist (please remove items if they don't apply):

• Code has been reviewed
• Functionality has been tested
• Windows installer (GH artifact) has been tested (installed and worked)
• MacOSX installer (GH artifact) has been tested (installed and worked)

[wpotrzebowski]

I got en error when I tried to "Add Constraints" without any model being selected:
20:27:46 - ERROR: Traceback (most recent call last): File "sas/qtgui/Perspectives/Fitting/ConstraintWidget.py", line 1144, in showMultiConstraint File "sas/qtgui/Perspectives/Fitting/ComplexConstraint.py", line 46, in __init__ File "sas/qtgui/Perspectives/Fitting/ComplexConstraint.py", line 85, in setupWidgets File "sas/qtgui/Perspectives/Fitting/ComplexConstraint.py", line 111, in setupParamWidgets IndexError: list index out of range
but it is probably a separate issue

[wpotrzebowski]

The changes in the code look ok. I'tested on Mac and it works fine but it also worked before. Probably someone else with Windows machine should take a look at it.

[gonzalezma]

Functionality checked. Close button is now active in all the windows where previously was not.

[wpotrzebowski]

It seems that this can be merged?