ci: Skip most tests on image builder changes

The image builder is covered by the FPGA pipelines, so we can be less
stringent for the SW pipelines.

tools/changeset_testlist.yaml

@@ -36,6 +36,15 @@
     - uhd.docs
   include_content: comments
   stop: False
+# Image builder
+# Note the FPGA pipelines have their own rules around the image builder. For
+# UHD, we just run a build to make sure the package is not in a weird state.
+- re: ^host/python/uhd/rfnoc_utils/grc.py
+  add:
+    - uhd.build.linux
+- re: ^host/python/uhd/rfnoc_utils/
+  add:
+    - uhd.build.linux
 # Device-specific changes. These should trigger HW tests only on those devices
 # they affect. We start with daughterboard rules, then motherboard rules.
 - re: host/lib/usrp/dboard/zbx/