Fix Rack version guard in build_nested_query spec

The escaping of [ and ] was backported in Rack 3.0.2.

Author: jeremyevans

spec/rack/test/utils_spec.rb

@@ -63,7 +63,7 @@
     original = Rack::Test::Utils.override_build_nested_query
     Rack::Test::Utils.override_build_nested_query = true
     begin
-      query = if Gem::Version.new(Rack.release) < Gem::Version.new("3.1")
+      query = if Gem::Version.new(Rack.release) < Gem::Version.new("3.0.2")
                 'a[b]=c'
               else
                 'a%5Bb%5D=c'