Use a time HTML tag to display phases dates

Currently this change is barely beneficial (if at all), but it doesn't
harm and might be useful in some cases. For instance, the `datetime`
attributes generates a date containing time zone information, which the
text shown on the screen does not, and styling dates with CSS is now
easier.

app/components/admin/budget_phases/phases_component.rb

@@ -20,6 +20,6 @@ class Admin::BudgetPhases::PhasesComponent < ApplicationComponent
     end
 
     def formatted_date(time)
-      l(time.to_date) if time.present?
+      time_tag(time.to_date, format: :default) if time.present?
     end
 end