Use property for getting enumerated values

[tfarago]

On one of the machines, conda had pygobject==3.50.0 installed and there the enumerated properties become gi.repository.GObject.ParamSpecEnum instead of gobject.GParamSpec. The prop.default_value.__enum_values__ trick did not work anymore, because the default_value was an integer. This PR fixes it. However, I do now know if it will work on older versions of pygobject than 3.48.2 (which I tested). Code to reproduce:

import gi
gi.require_version('Uca', '2.0')
from gi.repository import GObject, GLib, Uca
manager = Uca.PluginManager()
uca = manager.get_camerah("mock", None)
for prop in uca.props:
    if hasattr(prop, "enum_class"):
    eprop = prop
    break 
type(eprop)
gi.repository.GObject.ParamSpecEnum

Check before merge

• HIKA PyGObject: 3.42.2
• ID19 PyGObject: 3.48.2
• IMAGE PyGObject: 3.48.2
• CL/CT lab

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.52%. Comparing base (64508fd) to head (a5c94ef).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #561   +/-   ##
=======================================
  Coverage   83.52%   83.52%           
=======================================
  Files         133      133           
  Lines       10718    10718           
=======================================
  Hits         8952     8952           
  Misses       1766     1766           

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[tfarago]

HIKA PyGObject: 3.42.2
ID19 PyGObject: 3.48.2
IMAGE PyGObject: 3.48.2