[gnome-runtime-images] Nightly: use 21.08 branch now that it got released

[Jordan Petridis <jpetridis src gnome org>]

commit 301f596ba00f2728757491d5e3113ffbafbaf1a0
Author: Jordan Petridis <jordan centricular com>
Date:   Fri Sep 3 23:07:02 2021 +0300

    Nightly: use 21.08 branch now that it got released

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 50373ee..59bb324 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -134,7 +134,7 @@ flat-manager-client:
 .vars_nightly:
   variables:
     BRANCH: master
-    FD_BRANCH: "21.08beta"
+    FD_BRANCH: "21.08"
     LLVM_VERSION: "12"
   rules:
     - if: "$CI_MERGE_REQUEST_ID"