[gimp] gitlab-ci: try to fix the CI for releases (and other CI pipelines).

[Jehan <jehanp src gnome org>]

commit 0cc2dedeb3132999a9a54a608d3e50b8f8decd7b
Author: Jehan <jehan girinstud io>
Date:   Sat Aug 20 11:17:44 2022 +0200

    gitlab-ci: try to fix the CI for releases (and other CI pipelines).

 .gitlab-ci.yml | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 711730eed0..1cff434081 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -226,12 +226,14 @@ gimp-distcheck-debian:
 
 gimp-meson-debian:
   rules:
-    # On commits except tags.
-    - if: '$CI_PIPELINE_SOURCE == "push" && $CI_COMMIT_TAG == null'
-    # On merge requests.
+    # On commits and merge requests.
+    - if: '$CI_PIPELINE_SOURCE == "push"'
     - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
+    # On releases.
+    - if: '$CI_COMMIT_TAG != null'
     # Custom builds though web GUI, API or schedules.
     - if: '$GIMP_CI_MESON_GCC != null'
+    - if: '$GIMP_CI_SOURCES != null'
   extends: .gimp-debian-base
   script:
     - meson _build