Update dependency sinatra to v4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
sinatra (source, changelog)	"~> 3.1" -> "~> 4.0"

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Release Notes

sinatra/sinatra (sinatra)

### [`v4.0.0`](https://togithub.com/sinatra/sinatra/blob/HEAD/CHANGELOG.md#400--2024-01-19) [Compare Source](https://togithub.com/sinatra/sinatra/compare/v3.2.0...v4.0.0) - New: Add support for Rack 3 ([#​1857]) - Note: you may want to read the [Rack 3 Upgrade Guide] - Require Ruby 2.7.8 as minimum Ruby version ([#​1993]) - Breaking change: Drop support for Rack 2 ([#​1857]) - Note: when using Sinatra to start the web server, you now need the `rackup` gem installed - Breaking change: Remove the `IndifferentHash` initializer ([#​1982]) - Breaking change: Disable `session_hijacking` protection by default ([#​1984]) - Breaking change: Remove `Rack::Protection::EncryptedCookie` ([#​1989]) - Note: cookies are still encrypted (by [`Rack::Session::Cookie`][Rack::Session::Cookie]) [#​1857]: https://togithub.com/sinatra/sinatra/pull/1857 [#​1993]: https://togithub.com/sinatra/sinatra/pull/1993 [#​1982]: https://togithub.com/sinatra/sinatra/pull/1982 [#​1984]: https://togithub.com/sinatra/sinatra/pull/1984 [#​1989]: https://togithub.com/sinatra/sinatra/pull/1989 [`Rack::Session::Cookie`]: https://togithub.com/rack/rack-session [Rack 3 Upgrade Guide]: https://togithub.com/rack/rack/blob/main/UPGRADE-GUIDE.md

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