chore: Namespace a class to avoid Zeitwerk error

Zeitwerk is the code loader in Rails. It expects files to define classes
by a convention that it explains very clearly:

Zeitwerk::NameError:
  expected file /home/runner/work/planner/planner/lib/services/event_calendar.rb to define constant Services::EventCalendar, but didn't

Author: olleolleolle

app/mailers/event_invitation_mailer.rb

@@ -34,7 +34,7 @@ def attending(event, member, invitation)
 
     require 'services/event_calendar'
     attachments['codebar.ics'] = { mime_type: 'text/calendar',
-                                   content: EventCalendar.new(@event).calendar.to_ical }
+                                   content: ServicesEventCalendar.new(@event).calendar.to_ical }
 
     subject = "Your spot to #{@event.name} has been confirmed."
 

lib/services/event_calendar.rb

@@ -1,4 +1,4 @@
-class EventCalendar
+class Services::EventCalendar
   attr_reader :event
 
   def initialize(event)