CI: use qemuarm64 for pending-updates report job

Instead of using the side-effect of gem5-arm64 pulling in many layers,
do it explicitly.

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

.gitlab-ci.yml

@@ -234,7 +234,7 @@ pending-updates:
   script:
     - rm -fr update-report
     # This configuration has all of the layers we need enabled
-    - kas shell ci/gem5-arm64.yml --command \
+    - kas shell ci/meta-openembedded.yml:ci/gem5-arm64.yml:ci/qemuarm64.yml --command \
       "$CI_PROJECT_DIR/scripts/machine-summary.py -t report -o $CI_PROJECT_DIR/update-report $($CI_PROJECT_DIR/ci/listmachines.py meta-arm meta-arm-bsp meta-gem5)"
   # Do this on x86 whilst the compilers are x86-only
   tags: