fix: support single array objects in parsePair method

[fraigo]

Description
Fixes #7096

Allow using a single-element object to support current syntax in documentation examples for Nested Substitutions (https://codeigniter4.github.io/userguide/outgoing/view_parser.html#nested-substitutions) and Cascading Data (https://codeigniter4.github.io/userguide/outgoing/view_parser.html#cascading-data)

This fix will convert the object into an array list with 1 element.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

Thank you for sending a PR.

You must GPG-sign your work, certifying that you either wrote the work or otherwise have the right to pass it on to an open-source project. See Developer's Certificate of Origin.
See https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md#signing

And please fix the coding style.
See https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md#php-style

We also need unit testing.
See https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md#unit-testing

[kenjis]

{vars}...{/vars} is for multiple data.
Why do you need to set a single data?

[kenjis]

No feedback. Closing.

If you still find this change useful, please submit another PR following the guidelines.
https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md

Thank you.