config/pipeline.yaml: Cover kselftest on -next by default

Since -next is where the currently active upstream development is it's one
of the more important suites to cover, add it as a default for kselftest.

Now that the legacy system is disabled we have a lot more bandwidth in the
labs so there should be less concern about this than there was during the
bringup of the pipeline.

Signed-off-by: Mark Brown <broonie@kernel.org>

Author: broonie

config/pipeline.yaml

@@ -1533,6 +1533,7 @@ jobs:
     rules: &kselftest-rules
       tree:
         - mainline
+        - next
         - stable-rc
 
   kselftest-cpufreq: