[29673] Avoid stale? with CSP nonces

Not all headers treat 304 responses equally, some do replay the CSP
headers from the original 200 GET, but we cannot rely on that.

If the header is not replayed, the frontend-cached nonces will not be
valid resulting in a CSP violation.

```
References:
w3c/webappsec-csp#161
https://bugs.chromium.org/p/chromium/issues/detail?id=174301
```

https://community.openproject.com/wp/29673

app/controllers/activities_controller.rb

@@ -52,30 +52,20 @@ def index
 
     events = @activity.events(@date_from, @date_to)
     censor_events_from_projects_with_disabled_activity!(events) unless @project
-
-    if events.empty? || stale?(etag: [@activity.scope,
-                                      @date_to,
-                                      @date_from,
-                                      @with_subprojects,
-                                      @author,
-                                      events.first,
-                                      User.current,
-                                      current_language,
-                                      DesignColor.overwritten])
-      respond_to do |format|
-        format.html do
-          @events_by_day = events.group_by { |e| e.event_datetime.in_time_zone(User.current.time_zone).to_date }
-          render layout: false if request.xhr?
-        end
-        format.atom do
-          title = l(:label_activity)
-          if @author
-            title = @author.name
-          elsif @activity.scope.size == 1
-            title = l("label_#{@activity.scope.first.singularize}_plural")
-          end
-          render_feed(events, title: "#{@project || Setting.app_title}: #{title}")
+
+    respond_to do |format|
+      format.html do
+        @events_by_day = events.group_by { |e| e.event_datetime.in_time_zone(User.current.time_zone).to_date }
+        render layout: false if request.xhr?
+      end
+      format.atom do
+        title = l(:label_activity)
+        if @author
+          title = @author.name
+        elsif @activity.scope.size == 1
+          title = l("label_#{@activity.scope.first.singularize}_plural")
         end
+        render_feed(events, title: "#{@project || Setting.app_title}: #{title}")
       end
     end