[gimp] gitlab-ci: fix (again!) the gitlab-ci.

[Jehan <jehanp src gnome org>]

commit f2c73f2840d661823472913afd8cb0a4cbc245c3
Author: Jehan <jehan girinstud io>
Date:   Wed May 26 19:58:52 2021 +0200

    gitlab-ci: fix (again!) the gitlab-ci.
    
    Argh! So it turns out that .publish_nightly template uses already an
    only: key so we cannot use rules: (on the other hand I guess using only:
    ourselves is alright and concatenate ours and the one in the template).
    
    Fixes:
    > jobs:flatpak-nightly config key may not be used with `rules`: only

 .gitlab-ci.yml | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 7edf460229..69eaf7f3f3 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -810,9 +810,12 @@ win32-nightly:
 flatpak-nightly:
   extends: '.publish_nightly'
   stage: distribution
-  rules:
-    # Custom builds though web GUI, API or schedules.
-    - if: '$GIMP_CI_FLATPAK != null'
+  only:
+    variables:
+      # Custom builds though web GUI, API or schedules.
+      # I don't use 'rules:' because .publish_nightly template uses an
+      # 'only:' already which clashes with 'rules:'.
+      - $GIMP_CI_FLATPAK != null
   needs: ["flatpak"]
   dependencies:
     - 'flatpak'