[cantarell-fonts] Use Python 3.8 because we'd need gcc for pyclipper

[Nikolaus Waxweiler <nwaxweiler src gnome org>]

commit b397b041a036a451ff2ccc3d058b7025ac13ef7e
Author: Nikolaus Waxweiler <madigens gmail com>
Date:   Sun Dec 20 21:48:35 2020 +0000

    Use Python 3.8 because we'd need gcc for pyclipper

 .gitlab-ci.yml | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 84e7025f..e5ea0b37 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,7 +1,10 @@
 build:
   image: 'registry.fedoraproject.org/fedora:latest'
   script:
-    - dnf install -y git-core python3-pip meson ninja-build libappstream-glib-devel gettext
+    - dnf install -y git-core python3-pip meson ninja-build libappstream-glib-devel gettext python3.8
+    - python3.8 -m ensurepip
+    - python3.8 -m venv venv
+    - . venv/bin/activate
     - pip3 install meson ninja -r requirements.txt
     - meson build
     - ninja -C build install