Point CI testing multibranch job to staging branch

Check out CI scripts from staging/pr-ci-testing instead of master.

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
Change-Id: Iabfc0c0909d03247ed333382c35a080159960d6c
diff --git a/mbed-tls-restricted-pr-ci-testing.yaml b/mbed-tls-restricted-pr-ci-testing.yaml
index b07ef2a..d3a03fb 100644
--- a/mbed-tls-restricted-pr-ci-testing.yaml
+++ b/mbed-tls-restricted-pr-ci-testing.yaml
@@ -30,7 +30,7 @@
                       </traits>
                     </scm>
                   </retriever>
-                  <defaultVersion>master</defaultVersion>
+                  <defaultVersion>staging/pr-ci-testing</defaultVersion>
                   <implicit>true</implicit>
                   <allowVersionOverride>true</allowVersionOverride>
                   <includeInChangesets>true</includeInChangesets>