[4.6] fix: add validation message for min_dims

[christianberkman]

Description
Add missing validation message for min_dims validation rule introduced in #8966

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]

Please add it in the changelog "Message Changes".
https://github.com/codeigniter4/CodeIgniter4/blob/4.6/user_guide_src/source/changelogs/v4.6.0.rst#message-changes
E.g., https://codeigniter4.github.io/CodeIgniter4/changelogs/v4.5.0.html#message-changes

docs needed

[kenjis]

@christianberkman Thank you!