avoid fatal tb on bad fqcn callback name (#69440)

changelogs/fragments/no_fatal_bad_cb.yml

@@ -0,0 +1,2 @@
+bugfixes:
+    - avoid fatal traceback when a bad FQCN for a callback is supplied in the whitelist (#69401).

lib/ansible/executor/task_queue_manager.py

@@ -162,8 +162,11 @@ class TaskQueueManager:
         for callback_plugin_name in (c for c in C.DEFAULT_CALLBACK_WHITELIST if AnsibleCollectionRef.is_valid_fqcr(c)):
             # TODO: need to extend/duplicate the stdout callback check here (and possible move this ahead of the old way
             callback_obj = callback_loader.get(callback_plugin_name)
+            if callback_obj:
                 callback_obj.set_options()
                 self._callback_plugins.append(callback_obj)
+            else:
+                display.warning("Skipping '%s', unable to load or use as a callback" % callback_plugin_name)
 
         self._callbacks_loaded = True
 

test/integration/targets/collections/runme.sh

@@ -71,3 +71,6 @@ if [[ "$(grep -wc "dynamic_host_a" "$CACHEFILE")" -ne "0" ]]; then
 fi
 
 ./vars_plugin_tests.sh
+
+# ensure non existing callback does not crash ansible
+ANSIBLE_CALLBACK_WHITELIST=charlie.gomez.notme ansible -m ping localhost