Remove/Replace Rack::Utils::HeaderHash

[nari]

Happened warning log: warning: Rack::Utils::HeaderHash is deprecated and will be removed in Rack 3.1, switch to Rack::Headers in the rack-dev-mark-0.7.11/lib/rack/dev-mark/middleware.rb:21 when I update rails 7.1.0

The Rack::Utils::HeaderHash was removed by Rack on the commit: https://github.com/rack/rack/commit/a5762cf60af474b89b555ff8d151be5a021701f8#diff-85960cbd609e7f51a9881d1876b82d748f4ba8312a31e3329a5bb9bf791c60be

[mishina2228]

#68 has been merged so this can be closed.

[dtaniwaki]

Thank you!