tests/nested/manual/uc-update-assets-secure-add-sbat: do not run for …

…uc24+ (canonical#14286)

There is no point to test this case on uc24 or later, we already have
an sbat, and it is unlikely any UC24 will boot without one.  Also it
becomes difficult to build an old version on shim on newer GCC.

tests/nested/manual/uc-update-assets-secure-add-sbat/task.yaml

@@ -4,7 +4,11 @@ details: |
   This will happen on UC20 and we need to make sure that it will
   continue to boot.
 
-systems: [ubuntu-2*]
+# There is no point to test this case on uc24 or later, we already
+# have an sbat, and it is unlikely any UC24 will boot without one.
+# Also it becomes difficult to build an old version on shim on newer
+# GCC.
+systems: [ubuntu-20.04-64, ubuntu-22.04-64]
 
 environment:
   NESTED_ENABLE_SECURE_BOOT: true