[gnome-runtime-images] Fix typo

[Jordan Petridis <jpetridis src gnome org>]

commit af09d703eeb00853c9088767a9b97fd86879acee
Author: Jordan Petridis <jordan centricular com>
Date:   Thu Jul 7 21:53:14 2022 +0300

    Fix typo

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 8aa9dd1..1d208ad 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -115,7 +115,7 @@ flat-manager-client:aarch64:
               # This is for backwards compatibility
               if [ $ARCH == "x86_64" ]; then
                   # Tag `x86_64` also without the ARCH to not break the old path
-                  export OLD_TAG="${CI_REGISTRY_IMAGE}/gnome:${BRANCH}"
+                  export TAG_OLD="${CI_REGISTRY_IMAGE}/gnome:${BRANCH}"
                   buildah tag $TAG $TAG_OLD
                   buildah push $TAG_OLD
               fi