Fix DateTime comparison with DateTime::Infinity object

Fixes #16406

activesupport/CHANGELOG.md

+*   Fix DateTime comparison with DateTime::Infinity object.
+
+    *Rafael Mendonça França*
+
 *   Added Object#itself which returns the object itself. Useful when dealing with a chaining scenario, like Active Record scopes:
 
         Event.public_send(state.presence_in([ :trashed, :drafted ]) || :itself).order(:created_at)

activesupport/lib/active_support/core_ext/date_time/calculations.rb

@@ -161,7 +161,9 @@ def utc_offset
   # Layers additional behavior on DateTime#<=> so that Time and
   # ActiveSupport::TimeWithZone instances can be compared with a DateTime.
   def <=>(other)
-    if other.respond_to? :to_datetime
+    if other.kind_of?(Infinity)
+      super
+    elsif other.respond_to? :to_datetime
       super other.to_datetime
     else
       nil

activesupport/test/core_ext/range_ext_test.rb

@@ -16,6 +16,7 @@ def test_to_s_from_times
   def test_date_range
     assert_instance_of Range, DateTime.new..DateTime.new
     assert_instance_of Range, DateTime::Infinity.new..DateTime::Infinity.new
+    assert_instance_of Range, DateTime.new..DateTime::Infinity.new
   end
 
   def test_overlaps_last_inclusive