dev-yay: override Python interpreter for core tasks to ensure AUR builder compatibility

This change sets ansible_python_interpreter to /usr/bin/python3 when including
01_core.yml. It avoids permission issues when Ansible runs module-based tasks
as the non-privileged AUR builder user, since the virtualenv Python binary is
not executable for that user.

Context and discussion:
https://chatgpt.com/share/6930230d-d7e0-800f-a5dc-67d7f75020e5

roles/dev-yay/tasks/main.yml

@@ -1,2 +1,4 @@
 - include_tasks: 01_core.yml
+  vars:
+    ansible_python_interpreter: /usr/bin/python3
   when: run_once_dev_yay is not defined