examples/python: fix "import gi" in example

Otherwise there is a warning:

  from gi.repository import GLib, NM
  __main__:1: PyGIWarning: NM was imported without specifying a version first. Use gi.require_version(NM, 1.0) before import to ensure that the right version gets loaded.

examples/python/gi/get-devices.py

@@ -21,6 +21,8 @@
 
 # This example lists all devices, both real and placeholder ones
 
+import gi
+gi.require_version('NM', '1.0')
 from gi.repository import GLib, NM
 
 if __name__ == "__main__":