Fix Sinatra warning during specs

Some specs now print the following warning:

```
/path/to/bundler/tmp/1/gems/base/ruby/3.2.0/gems/sinatra-2.0.8.1/lib/sinatra/base.rb:902: warning: constant Tilt::Cache is deprecated
```

Updating sinatra to latest & greatest fixes it.

Update other deps too since at it.

tool/bundler/test_gems.rb

@@ -2,11 +2,11 @@
 
 source "https://rubygems.org"
 
-gem "rack", "2.0.8"
+gem "rack", "~> 2.0"
 gem "webrick", "1.7.0"
 gem "rack-test", "~> 1.1"
 gem "compact_index", "~> 0.15.0"
-gem "sinatra", "~> 2.0"
+gem "sinatra", "~> 3.0"
 gem "rake", "~> 13.1"
 gem "builder", "~> 3.2"
 gem "rb_sys"