fix(raspberrypi): detect Raspberry Pi hardware in check mode (#719)

- set check_mode: false on the /proc/cpuinfo and /proc/device-tree/model
  probes, since ansible.builtin.command never executes under --check and
  returns rc 0 with "Command would have run if not in check mode"
- default a missing probe rc to 1 in the raspberry_pi gate so an undefined
  result cannot be read as "this host is a Raspberry Pi"
- add a structural regression test and hook it into pre-commit

Without this, site.yml --check marked every x86_64 host as a Raspberry Pi and
applied the distro specific setup tasks, failing on Ubuntu with
"Destination /boot/firmware/cmdline.txt does not exist".

.pre-commit-config.yaml

@@ -76,6 +76,12 @@ repos:
         language: system
         pass_filenames: false
         files: ^roles/prereq/(tasks/main|defaults/main)\.yml$|^\.github/scripts/test-disable-swap\.sh$
+      - id: raspberrypi-detection-test
+        name: Raspberry Pi detection test
+        entry: .github/scripts/test-raspberrypi-detection.sh
+        language: system
+        pass_filenames: false
+        files: ^roles/raspberrypi/(tasks/main|defaults/main)\.yml$|^\.github/scripts/test-raspberrypi-detection\.sh$
       - id: cilium-bgp-manifest-test
         name: Cilium BGP manifest test
         entry: python3 .github/scripts/test-cilium-bgp-manifest.py