Merge pull request rails#49740 from y-yagi/donot-use-deprecated-to_default_s

Don't use deprecated `#to_default_s` in `Date#to_fs`

Author: kamipo

activesupport/lib/active_support/core_ext/date/conversions.rb

@@ -52,7 +52,7 @@ def to_fs(format = :default)
         strftime(formatter)
       end
     else
-      to_default_s
+      to_s
     end
   end
   alias_method :to_formatted_s, :to_fs

activesupport/test/core_ext/date_ext_test.rb

@@ -37,6 +37,7 @@ def test_to_fs
     assert_equal "2005-02-21",          date.to_fs(:inspect)
     assert_equal "21 Feb 2005",         date.to_fs(:rfc822)
     assert_equal "2005-02-21",          date.to_fs(:iso8601)
+    assert_equal date.to_s,             date.to_fs(:doesnt_exist)
     assert_equal "21 Feb",              date.to_formatted_s(:short)
   end