cobbler_system: fix KeyError when adding new interface to existing system (#11995)

* fix(cobbler_system): handle missing interface device on existing system

When adding a new interface to an existing Cobbler system that does not
yet have that interface defined, the module raised a KeyError. Use .get()
with a fallback empty dict to safely handle that case. Also add a
continue after the unknown-property warning to prevent a secondary
KeyError on IFPROPS_MAPPING lookup.

Fixes: #7007

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* chore(cobbler_system): add changelog fragment for #11995

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

changelogs/fragments/11995-cobbler-system-interface-keyerror.yml

@@ -0,0 +1,4 @@
+bugfixes:
+  - cobbler_system - fix ``KeyError`` when adding a new interface to an existing system that does not yet have it defined
+    (https://github.com/ansible-collections/community.general/issues/7007,
+    https://github.com/ansible-collections/community.general/pull/11995).

plugins/modules/cobbler_system.py

@@ -298,7 +298,8 @@ def main():
                         continue
                     if key not in IFPROPS_MAPPING:
                         module.warn(f"Property '{key}' is not a valid system property.")
-                    if not system or system["interfaces"][device][IFPROPS_MAPPING[key]] != value:
+                        continue
+                    if not system or system["interfaces"].get(device, {}).get(IFPROPS_MAPPING[key]) != value:
                         result["changed"] = True
                     interface_properties[f"{key}-{device}"] = value