Oops, add EXECJS_RUNTIME=Disabled to service file

Uhhh I think I must have made a mistake here where like… I must have left this in the service file for a while then accidentally deleted it from the Ansible playbook but not the live server? I had tested with this, then tested again without it and thought it wasn't necessary, but it turns out to have been necessary I guess? Ok!

This instructs Rails's ExecJS library to not bother looking for Node or something similar, because the app doesn't actually need to run any JS, even though the `react-rails` library (?) seems to be pretty eager about the possibility that we'll need to server-side-render stuff. (We should consider whether we want to though tbh? But… idk that would be a pretty different arch than what we've done with `jsbundling-rails` so like. idk whatever)

deploy/setup.yml

@@ -252,6 +252,7 @@
           WorkingDirectory=/srv/impress/current
           ExecStart=/opt/ruby-3.1.4/bin/bundle exec puma --port=3000
           Environment="RAILS_ENV=production"
+          Environment="EXECJS_RUNTIME=Disabled" ; to save us from installing Node
           EnvironmentFile=/srv/impress/shared/production.env
 
           ; Some security directives, adapted from Akkoma's service file, they seem like sensible defaults!