Split runner into own playbook to prevent self-restart during CI

.gitea/workflows/ansible.yml

@@ -14,6 +14,7 @@ on:
         type: choice
         options:
           - infra.yml
+          - runner.yml
 
 jobs:
   ansible:

ansible/infra.yml

@@ -5,6 +5,5 @@
 
   roles:
     - gitea
-    - gitea-runner
     - vaultwarden
     - backup

ansible/runner.yml

@@ -0,0 +1,7 @@
+---
+- name: Set up Gitea runner
+  hosts: infra
+  become: true
+
+  roles:
+    - gitea-runner