Always issue deprecation warning when calling Regexp.new with 3rd pos…

…itional argument

Previously, only certain values of the 3rd argument triggered a
deprecation warning.

First step for fix for bug #18797.  Support for the 3rd argument
will be removed after the release of Ruby 3.2.

Fix minor fallout discovered by the tests.

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

lib/racc/statetransitiontable.rb

@@ -216,7 +216,7 @@ def mkmapexp(arr)
         end
         i = ii
       end
-      Regexp.compile(map, nil, 'n')
+      Regexp.compile(map, Regexp::NOENCODING)
     end
 
     def set_table(entries, dummy, tbl, chk, ptr)