[gnome-runtime-images] ci: add llvm version var to the stable jobs

[Jordan Petridis <jpetridis src gnome org>]

commit e95adb4cf04c14b7445810ec7c7238d43c60793a
Author: Jordan Petridis <jordan centricular com>
Date:   Mon Oct 18 04:40:56 2021 +0300

    ci: add llvm version var to the stable jobs

 .gitlab-ci.yml | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 2308d29..5dd948f 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -119,6 +119,7 @@ flat-manager-client:
   variables:
     BRANCH: "40"
     FD_BRANCH: "20.08"
+    LLVM_VERSION: "12"
   rules:
     - if: '$REBUILD_STABLE'
       when: 'always'
@@ -129,6 +130,7 @@ flat-manager-client:
   variables:
     BRANCH: "41"
     FD_BRANCH: "21.08"
+    LLVM_VERSION: "12"
   rules:
     - if: '$REBUILD_STABLE'
       when: 'always'