[polari] ci: Prepare for switch of default branch

[Florian Müllner <fmuellner src gnome org>]

commit 8e0b35db84bd631f19a3eccae9e5ffd80be5ddda
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Jul 13 19:06:37 2021 +0200

    ci: Prepare for switch of default branch
    
    Using 'rules' instead of 'only'/'except' allows us to refer to the
    default branch by variable instead of hardcoding its name.
    
    https://gitlab.gnome.org/GNOME/polari/-/merge_requests/202

 .gitlab-ci.yml | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 50b89ce1..97241182 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -103,13 +103,13 @@ flatpak:
         BRANCH: "snapshot"
         CONFIG_OPTS: "-Dsnapshot=true --werror --warnlevel 2"
     extends: .flatpak-template
-    except:
-        - master
+    rules:
+        - if: '$CI_COMMIT_BRANCH != $CI_DEFAULT_BRANCH'
 
-flatpak-master:
+flatpak-main:
     extends: .flatpak-template
-    only:
-        - master
+    rules:
+        - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH'
 
 nightly:
   extends: '.publish_nightly'