Respect Regexp.compile method signature

As far as I can tell, Regexp.compile has never accepted a third
parameter to Regexp.compile until Ruby 3.2. There it actually is a
timeout parameter. In older versions it was discarded as an invalid
input. It's unclear to me if this parameter ever worked in the first
place.

This PR attemps to still make it work as it was originally intended, but
it's unclear what the original goal even was.

lib/puppet/functions/regsubst.rb

@@ -56,13 +56,10 @@
  # - *I* Ignore case in regexps
  # - *M* Multiline regexps
  # - *G* Global replacement; all occurrences of the regexp in each target string will be replaced. Without this, only the first occurrence will be replaced.
- # @param encoding [Enum['N','E','S','U']]
+ # @param encoding [Optional[Enum['N']]
  # Optional. How to handle multibyte characters when compiling the regexp (must not be used when pattern is a
  # precompiled regexp). A single-character string with the following values:
  # - *N* None
- # - *E* EUC
- # - *S* SJIS
- # - *U* UTF-8
  # @return [Array[String], String] The result of the substitution. Result type is the same as for the target parameter.
  # @example Put angle brackets around each octet in the node's IP address:
  # ```puppet
@@ -85,10 +82,11 @@ def regsubst_string(target, pattern, replacement, flags = nil, encoding = nil)
  when 'E' then re_flags |= Regexp::EXTENDED
  when 'I' then re_flags |= Regexp::IGNORECASE
  when 'M' then re_flags |= Regexp::MULTILINE
+ when 'N' then re_flags |= Regexp::NOENCODING
  end
  end
  end
- inner_regsubst(target, Regexp.compile(pattern, re_flags, encoding), replacement, operation)
+ inner_regsubst(target, Regexp.compile(pattern, re_flags), replacement, operation)
  end
 
  def regsubst_regexp(target, pattern, replacement, flags = nil)