Fix issue with regression in integration tests when providing as: :html

[mguan2020]

Motivation / Background

This Pull Request has been created in order to fix issue #50345.

Detail

This Pull Request solves the problem in Rails 7.1 where providing as: :html in the integration test for ActionDispatch causes a "undefined method to_html" error to be thrown.

To solve this issue, this Pull Request registers a param_encoder in addition to a HTML encoder in order to perform the request to the controller.

As a result, both the new tests provided in content_type_test.rb as well as the original tests for ActionDispatch are working.

Additional information

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[seanpdoyle]

I think the fix requires more changes than what's proposed in this diff. I've opened #50390 as an alternative resolution to the issue.