nginx update v1.21.2

http://nginx.org/en/CHANGES

roles/matrix-nginx-proxy/defaults/main.yml

 matrix_nginx_proxy_enabled: true
-matrix_nginx_proxy_version: 1.21.1-alpine
+matrix_nginx_proxy_version: 1.21.2-alpine
 
 # We use an official nginx image, which we fix-up to run unprivileged.
 # An alternative would be an `nginxinc/nginx-unprivileged` image, but