Remove limit on PySide6 version

We had issues with PySide6 version 6.8.0, but the latest version,
version 6.8.1, appears to be working fine.

Signed-off-by: Patrick Avery <patrick.avery@kitware.com>

setup.py

@@ -7,9 +7,7 @@
     'fabio>=0.11',
     'matplotlib',
     'Pillow',
-    # PySide 6.8.0 is causing segmentation faults in the testing
-    # Keep this version downgraded until that is fixed.
-    'pyside6<6.8.0',
+    'pyside6',
     'pyyaml',
     'silx',
 ]