tests(bk): Run the kernel build in our nightly PR

Run the kernel build as part of our nightly tests so we can monitor it's
success.

Signed-off-by: Jack Thomson <[email protected]>

Author: JackThomson2

.buildkite/pipeline_pr.py

@@ -68,7 +68,7 @@
     for step in kani_grp["steps"]:
         step["label"] = "🔍 Kani"
 
-if any(x.parent.name == "hiding_ci" for x in changed_files):
+if not changed_files or (any(x.parent.name == "hiding_ci" for x in changed_files)):
     pipeline.build_group_per_arch(
         "🕵️ Build Secret Hiding Kernel",
         pipeline.devtool_test(