Use URI::RFC2396_Parser#regex explicitly.

[hsbt]

I got the following error with the current develop version of ruby/ruby.

  87) Mustermann::Template level 4 operator + pattern "/{a}/{+b}" is expected to expand {:a=>"foo/bar", :b=>"foo/bar"}
      Failure/Error: it { should expand(a: 'foo/bar', b: 'foo/bar').to('/foo%2Fbar/foo/bar') }

      TypeError:
        no implicit conversion of nil into String
      # ./mustermann/lib/mustermann/ast/translator.rb:122:in 'Regexp.union'

In background, URI will change DEFAULT_PARSER to RFC3986_Parser.

ruby/uri#107

After that, we lost some of regex pattern like UNSAFE.

[dentarg]

LGTM

root@a48d10429c21:/# ruby -v
ruby 2.6.10p210 (2022-04-12 revision 67958) [aarch64-linux]
root@a48d10429c21:/#
root@a48d10429c21:/# ruby -e 'p URI::RFC2396_Parser.new.regexp[:UNSAFE]'
/[^\-_.!~*'()a-zA-Z\d;\/?:@&=+$,\[\]]/

[dentarg]

Looks like there is a constant URI::RFC2396_PARSER that could be used in Ruby 3.4+ https://github.com/octokit/octokit.rb/pull/1708/files

[dentarg]

Released in v3.0.1

[hsbt]

@dentarg Thanks!