[gitg] Revert "libgitg-ext/meson.build: Use python module instead of deprecated python3 module"

[Alberto Fanjul <albfan src gnome org>]

commit 86b708ff559fa4f3bc7858f6c2c03afd493817da
Author: Alberto Fanjul <albertofanjul gmail com>
Date:   Thu Apr 4 22:45:06 2019 +0200

    Revert "libgitg-ext/meson.build: Use python module instead of deprecated python3 module"
    
    This breaks compilation in flatpak

 libgitg-ext/meson.build | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
---
diff --git a/libgitg-ext/meson.build b/libgitg-ext/meson.build
index cb2bebe2..f116ba01 100644
--- a/libgitg-ext/meson.build
+++ b/libgitg-ext/meson.build
@@ -125,11 +125,10 @@ custom_target(
 
 enable_python = get_option('python')
 if enable_python
-  pymod = import('python')
-  py_installation = pymod.find_installation('python3')
+  python = import('python3')
 
   install_data(
     'GitgExt.py',
-    install_dir: join_paths(py_installation.get_path('purelib'), 'gi', 'overrides'),
+    install_dir: join_paths(python.sysconfig_path('purelib'), 'gi', 'overrides'),
   )
 endif