[libxslt] Add CI test for Python 3

[Nick Wellnhofer <nwellnhof src gnome org>]

commit f8664f61aa422225de3b717c1504ef4df3643655
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Thu Nov 19 17:17:09 2020 +0100

    Add CI test for Python 3

 .gitlab-ci.yml | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a9fa1425..804ff156 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -26,6 +26,12 @@ gcc:
   variables:
     CFLAGS: "-O2 -std=c89 -D_POSIX_C_SOURCE=200112L"
 
+gcc:python3:
+  extends: .test
+  variables:
+    CONFIG: "--with-python=/usr/bin/python3"
+    CFLAGS: "-O2"
+
 clang:asan:
   extends: .test
   variables: