[gimp-macos-build/wip/Jehan/path-max-issue-424] Use Python 3.8!

[Jehan <jehanp src gnome org>]

commit b33e4b6ae68b1f86b5bdc14c209a83a520d338d3
Author: Jehan <jehan girinstud io>
Date:   Fri Jul 23 21:48:42 2021 +0200

    Use Python 3.8!

 jhbuildrc-gtk-osx-gimp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/jhbuildrc-gtk-osx-gimp b/jhbuildrc-gtk-osx-gimp
index 8fefc5b..2d4a36d 100644
--- a/jhbuildrc-gtk-osx-gimp
+++ b/jhbuildrc-gtk-osx-gimp
@@ -160,8 +160,9 @@ moduleset = 'https://gitlab.gnome.org/samm-git/gtk-osx/raw/wip/Jehan/path-max-is
 # force python 3.6 for the libxml2 to avoid build issues
 module_extra_env['libxml2'] = { "ac_cv_path_PYTHON": "python3.6" }
 
-# force python 3.6 for gimp-help.
-module_extra_env['gimp-help-git'] = { "PYTHON": "python3.6" }
+# force python 3.8 for gimp-help because libxml2 is built with Python
+# 3.8 support.
+module_extra_env['gimp-help-git'] = { "PYTHON": "python3.8" }
 
 # meson needs UTF-8 charset for build python scripts to work correctly
 module_extra_env['meson'] = { "LC_ALL": "en_US.UTF-8" }