tf-a-lts2.8-tftf-gerrit-tforg-l1,2: Explicitly set TF_GERRIT_BRANCH

Similar to tf-a-lts2.8-main.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I378a723a6e5047fb799b59c5442e108c6ed3dbab
diff --git a/tf-a-lts2.8-tftf-gerrit-tforg-l1.yaml b/tf-a-lts2.8-tftf-gerrit-tforg-l1.yaml
index f00a3eb..1274880 100644
--- a/tf-a-lts2.8-tftf-gerrit-tforg-l1.yaml
+++ b/tf-a-lts2.8-tftf-gerrit-tforg-l1.yaml
@@ -33,6 +33,9 @@
             name: GERRIT_CHANGE_NUMBER
             default: ''
         - string:
+            name: TF_GERRIT_BRANCH
+            default: 'refs/heads/lts-v2.8'
+        - string:
             name: TF_GERRIT_REFSPEC
             default: '+refs/heads/lts-v2.8:refs/remotes/origin/lts-v2.8'
         - string: