devel/shiboken2: limit supported python versions

With python 3.10:

pyside-setup-opensource-src-5.15.2/sources/shiboken2/libshiboken/pep384impl.cpp:755:12: error: use of undeclared identifier '_Py_Mangle'

return _Py_Mangle(privateobj, name);
       ^

pyside-setup-opensource-src-5.15.2/sources/shiboken2/libshiboken/sbkstring.cpp:250:23: error: expression is not assignable

Py_REFCNT(ob) = 1;
~~~~~~~~~~~~~ ^

Also mark BROKEN with python < 3.8 due to plist issues

Approved by: portmgr blanket