CI: use scarthgap branches

Upstream master and scarthgap have now diverged, so use scarthgap whilst
we prepare for release.  At the time of writing there is no scarthgap
branch for meta-clang, so leave that on master.

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

ci/base.yml

@@ -5,7 +5,7 @@ distro: poky
 
 defaults:
   repos:
-    branch: master
+    branch: scarthgap
 
 repos:
   meta-arm:

ci/clang.yml

@@ -4,6 +4,7 @@ header:
 repos:
   meta-clang:
     url: https://github.com/kraj/meta-clang
+    branch: master
 
 local_conf_header:
   toolchain: |