tf-m-release.yaml: Switch back to master branch

TF-M v1.8.0 release test has been finished. So switch the default
branches back to master branch for the regular verification.

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I0a40eabd7c6b50ff259d94a2bcfa07b282c9cdd7
diff --git a/tf-m-release.yaml b/tf-m-release.yaml
index 6bb9aa9..fb5b996 100644
--- a/tf-m-release.yaml
+++ b/tf-m-release.yaml
@@ -39,7 +39,7 @@
           default: 'master'
       - string:
           name: 'GERRIT_REFSPEC'
-          default: 'release/1.8.x'
+          default: 'refs/heads/master'
           description: |
             For use when triggering with specified tag or master 'refs/heads/master' or 'refs/tags/TF-Mv1.0'.
       - string:
@@ -100,7 +100,7 @@
           default: 'https://git.trustedfirmware.org/TF-M/tf-m-tests.git'
       - string:
           name: 'TFM_TESTS_REFSPEC'
-          default: 'release/1.8.x'
+          default: 'refs/heads/master'
           description: |
             Specify which tf-m-tests version to use
             refs/heads/<branch_name> : Pick up latest HEAD on branch