PluginManager: Load plugins on Windows correctly

On Windows we ship compiled files
3 jobs for gajim_1.2 in 4 minutes and 26 seconds (queued for 1 minute and 55 seconds)
Status Job ID Name Coverage
  Test
passed #17646
run-appdata

00:00:06

passed #17645
run-tests

00:04:08

 
  Build
passed #17647
run-build

00:00:11