CI: use walnascar branches

Signed-off-by: Ross Burton <ross.burton@arm.com>

ci/base.yml

@@ -7,7 +7,7 @@ distro: poky
 
 defaults:
   repos:
-    branch: master
+    branch: walnascar
 
 repos:
   meta-arm:

ci/meta-virtualization.yml

@@ -8,3 +8,4 @@ header:
 repos:
   meta-virtualization:
     url: https://git.yoctoproject.org/meta-virtualization
+    branch: master