Make tests pass on JRuby 9.4

[dentarg]

We allow them to fail currently:

sinatra/.github/workflows/test.yml

Lines 41 to 42 in 0a424f0

	# Due to https://github.com/jruby/jruby/issues/7647
	- { ruby: jruby-9.4, rack: '~> 2', puma: stable, tilt: '~> 2.0.0', allow-failure: true }

I thought it was a problem with JRuby, so I reported jruby/jruby#7647, but as seen in that issue, it is not, the problem is with rack: rack/rack#1610 (missing delegate require) It is fixed in Rack 3, but will likely never be fixed for Rack 2.

(This wasn't a problem with JRuby 9.3 because the missing delegate require is only a problem in Ruby versions >2.6: jruby/jruby#7647 (comment))

It is still a mystery to me why only the JRuby tests fail though 🤔 I would really appreciate someone explaining that

[dentarg]

Rack backport PR: rack/rack#2092

[dentarg]

Rack backport PR: rack/rack#2092

It is part of rack 2.2.8 released today: https://rubygems.org/gems/rack/versions/2.2.8

[dentarg]

Yeah, rack 2.2.8 resolved this, JRuby 9.4 tests pass here: https://github.com/dentarg/sinatra/actions/runs/5753078429/job/15595497187#step:7:17

And they failed here with rack 2.2.7: https://github.com/dentarg/sinatra/actions/runs/5576942970/job/15101401844#step:7:43