JRuby/HEAD tests failing

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JRuby tests are failing, see https://github.com/ruby-grape/grape-swagger-rails/actions/runs/8030570532/job/21938077626

@SofiaSousa mind taking a look? it's likely unrelated to your latest PR.

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Fetching gem metadata from https://rubygems.org/...........
Resolving dependencies...
Could not find compatible versions

Because every version of grape-swagger depends on Ruby >= 3.0
  and Gemfile depends on grape-swagger >= 0,
  Ruby >= 3.0 is required.
So, because current Ruby version is = 2.7.8,
  version solving has failed.
Error: The process '/opt/hostedtoolcache/Ruby/2.7.8/x64/bin/bundle' failed with exit code 6

Another failure in the matrix, #116