Both `Nokogiri` and `Minitest` have merged the PRs mentioned to
integrate support for Ruby's Pattern matching
(https://github.com/sparklemotion/nokogiri/pull/2523 and
https://github.com/minitest/minitest/pull/936, respectively).

This commit adds coverage for those new assertions, and incorporates
examples into the documentation for the `response.parsed_body` method.

In order to incorporate pattern-matching support for JSON responses,
this commit changes the response parser to call `JSON.parse` with
[object_class: ActiveSupport::HashWithIndifferentAccess][object_class],
since String instances for `Hash` keys are incompatible with Ruby's
syntactically pattern matching.

For example:

```ruby
irb(main):001:0> json = {"key" => "value"}
=> {"key"=>"value"}
irb(main):002:0> json in {key: /value/}
=> false

irb(main):001:0> json = {"key" => "value"}
=> {"key"=>"value"}
irb(main):002:0> json in {"key" => /value/}
.../3.2.0/lib/ruby/gems/3.2.0/gems/irb-1.7.4/lib/irb/workspace.rb:113:in `eval': (irb):2: syntax error, unexpected terminator, expecting literal content or tSTRING_DBEG or tSTRING_DVAR or tLABEL_END (SyntaxError)
json in {"key" => /value/}
             ^

        .../ruby/3.2.0/lib/ruby/gems/3.2.0/gems/irb-1.7.4/exe/irb:9:in `<top (required)>'
        .../ruby/3.2.0/bin/irb:25:in `load'
        .../ruby/3.2.0/bin/irb:25:in `<main>'
```

When the Hash maps String keys to Symbol keys, it's able to be pattern
matched:

```ruby
irb(main):005:0> json = {"key" => "value"}.with_indifferent_access
=> {"key"=>"value"}
irb(main):006:0> json in {key: /value/}
=> true
```

[object_class]: https://docs.ruby-lang.org/en/3.2/JSON.html#module-JSON-label-Parsing+Options