Load roles/matrix-synapse/vars/workers.yml earlier to not break --tags=setup-nginx-proxy

If we load it at runtime, during matrix-synapse role execution,
it's good enough for matrix-synapse and all roles after that,
but.. it breaks when someone uses `--tags=setup-nginx-proxy` alone.

The downside of including this vars file like this in `setup.yml`
is that the variables contained in it cannot be overriden by the user
(in their inventory's `vars.yml`).
... but it's not like overriding these variables was possible anyway
when including them at runtime.

roles/matrix-synapse/tasks/workers/setup_install.yml

@@ -1,8 +1,5 @@
 ---
 
-- name: Load list of available worker apps and endpoints
-  include_vars: "{{ role_path }}/vars/workers.yml"
-
 - name: Ensure synapse worker base service file installed
   template:
     src: "{{ role_path }}/templates/synapse/systemd/matrix-synapse-worker@.service.j2"

setup.yml

@@ -3,6 +3,9 @@
   hosts: "{{ target if target is defined else 'matrix_servers' }}"
   become: true
 
+  vars_files:
+    - roles/matrix-synapse/vars/workers.yml
+
   roles:
     - matrix-base
     - matrix-dynamic-dns