swig-rb: Fix fronzen string literal warnings since Ruby 3.4.

* subversion/bindings/swig/ruby/svn/core.rb
  (Stream#read,
   Stream#read_all,
   Config#to_s): Use `String.new` instead of string literal.
* subversion/bindings/swig/ruby/svn/error.rb
  (SvnError#initialize): Ditto.
* subversion/bindings/swig/ruby/svn/info.rb
  (DiffEntry#initialize): Ditto.
* subversion/bindings/swig/ruby/test/test_core.rb
  (SvnCoreTest#test_stream_copy): Ditto.
* subversion/bindings/swig/ruby/test/test_delta.rb
  (SvnDeltaTest#test_txdelta_apply_instructions,
   SvnDeltaTest#test_push_target,
   SvnDeltaTest#test_apply,
   SvnDeltaTest#test_svndiff): Ditto.
* subversion/bindings/swig/ruby/test/test_fs.rb
  (SvnFsTest#test_delta): Ditto.
* subversion/bindings/swig/ruby/test/test_repos.rb
  (SvnReposTest#test_dump,
   SvnReposTest#test_load): Ditto.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1933572 13f79535-47bb-0310-9956-ffa450edef68