Switch TF-M branch from "master" to "main"

TF-M development branch is going to be switched from "master" to "main".
Update CI settings to enable tests on "main" branch.

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I3cb37e0f777d117b4ed2081125cfcebd59ed7472
diff --git a/tf-m-eclair-delta.yaml b/tf-m-eclair-delta.yaml
index 1d77db8..55af62d 100644
--- a/tf-m-eclair-delta.yaml
+++ b/tf-m-eclair-delta.yaml
@@ -35,12 +35,12 @@
           default: 'master'
       - string:
           name: 'GERRIT_REFSPEC'
-          default: 'refs/heads/master'
+          default: 'refs/heads/main'
           description: |
-            For use when triggering with specified tag or master 'refs/heads/master' or 'refs/tags/TF-Mv1.0'.
+            For use when triggering with specified tag or master 'refs/heads/main' or 'refs/tags/TF-Mv1.0'.
       - string:
           name: 'GERRIT_BRANCH'
-          default: 'master'
+          default: 'main'
           description: |
             TF-M branch.
       - string: