build: fix PySide6 to 6.7.2
Description
Fix pyside6 to 6.7.2 as 6.8 is causing segfaults for testing.
Code indexing in gitaly is broken and leads to code not being visible to the user. We work on the issue with highest priority.
Please migrate repositories to https://gitea.psi.ch - if you need help, contact gitea@psi.ch