Revert "Rollback to released version numbers of stringio and strscan"

	This reverts commit 6a79e53823e328281b9e9eee53cd141af28f8548.

	[ruby/strscan] StringScanner#captures: Return nil not "" for unmached capture (https://github.com/ruby/strscan/pull/72)

	fix https://github.com/ruby/strscan/issues/70
	If there is no substring matching the group (s[3]), the behavior is
	different.

	If there is no substring matching the group, the corresponding element
	(s[3]) should be nil.

	```
	s = StringScanner.new('foobarbaz') #=> #<StringScanner 0/9 @ "fooba...">
	s.scan /(foo)(bar)(BAZ)?/  #=> "foobar"
	s[0]           #=> "foobar"
	s[1]           #=> "foo"
	s[2]           #=> "bar"
	s[3]           #=> nil
	s.captures #=> ["foo", "bar", ""]
	s.captures.compact #=> ["foo", "bar", ""]
	```

	```
	s = StringScanner.new('foobarbaz') #=> #<StringScanner 0/9 @ "fooba...">
	s.scan /(foo)(bar)(BAZ)?/  #=> "foobar"
	s[0]           #=> "foobar"
	s[1]           #=> "foo"
	s[2]           #=> "bar"
	s[3]           #=> nil
	s.captures #=> ["foo", "bar", nil]
	s.captures.compact #=> ["foo", "bar"]
	```

	https://docs.ruby-lang.org/ja/latest/method/MatchData/i/captures.html
	```
	/(foo)(bar)(BAZ)?/ =~ "foobarbaz" #=> 0
	$~.to_a        #=> ["foobar", "foo", "bar", nil]
	$~.captures #=> ["foo", "bar", nil]
	$~.captures.compact #=> ["foo", "bar"]
	```

	* StringScanner#captures is not yet documented.
	https://docs.ruby-lang.org/ja/latest/class/StringScanner.html

	https://github.com/ruby/strscan/commit/1fbfdd3c6f

	[ruby/strscan] Bump version

	https://github.com/ruby/strscan/commit/d6f97ec102

https://github.com/ruby/stringio/commit/75da93d48f

* Before this it was compiled but not used, because TruffleRuby has
  a stringio.rb in stdlib and .rb has precedence over .so.
  In fact that extension never worked on TruffleRuby,
  because rb_io_extract_modeenc() has never been defined on TruffleRuby.
* So this just skip compiling the extension since compilation of it now fails:
  https://github.com/ruby/openssl/issues/699

https://github.com/ruby/stringio/commit/d791b63df6

https://github.com/ruby/stringio/commit/a2f8ef1a6a

(https://github.com/ruby/stringio/pull/69)

The conversion logic is borrowed from ruby/ruby's io.c:
https://github.com/ruby/ruby/blob/40391faeab608665da87a05c686c074f91a5a206/io.c#L4059-L4079

Fix ruby/stringio#68

Reported by IWAMOTO Kouichi. Thanks!!!

https://github.com/ruby/stringio/commit/4b170c1a68

https://github.com/ruby/stringio/commit/4400bf3380

https://github.com/ruby/stringio/commit/3f90a0d619

(https://github.com/ruby/stringio/pull/67)

Fix: https://github.com/ruby/stringio/issues/66

If length is 0, IO#pread don't even try to read the IO, it simply return
the buffer untouched if there is one or a new empty buffer otherwise.

It also doesn't validate the offset when length is 0.

cc @jdelStrother @kou

https://github.com/ruby/stringio/commit/37e9279337

Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

(https://github.com/ruby/stringio/pull/65)

https://github.com/ruby/stringio/commit/e3ea087d04