CI: Use more specific Xilinx runner tags

In order to avoid serialising the testing on both boards, the runner
configuration is being adjusted.

Have the .xilinx-arm64 and .xilinx-x86_64 templates choose the board directly
using a more specific tag.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Victor Lira <victorm.lira@amd.com>
(cherry picked from commit efcb4c5e2f)

automation/gitlab-ci/test.yaml

@@ -94,7 +94,7 @@
     variables:
       - $XILINX_JOBS == "true" && $CI_COMMIT_REF_PROTECTED == "true"
   tags:
-    - xilinx
+    - xilinx-zynq-423
 
 .adl-x86-64:
   extends: .test-jobs-common