refactor: remove unnecessary is_countable() check in getMethodParams()

[datamweb]

Description
This PR optimizes the getMethodParams method by removing the unnecessary is_countable() check.

The preg_match_all() function guarantees that $matches will always be an array.
If no matches are found, $matches[0] will be an empty array, and the function will return 0.

See : https://github.com/codeigniter4/CodeIgniter4/actions/runs/11033764630/job/30645688529?pr=9202

 ------ --------------------------------------------------------------------- 
  Line   system/Router/RouteCollection.php                                    
 ------ --------------------------------------------------------------------- 
  1614   Call to function is_countable() with array<int, string> will always  
         evaluate to true.                                                    
         🪪  function.alreadyNarrowedType      

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

[datamweb]

@samsonasik Does Rector have any specific rules or guidelines regarding this matter?

[samsonasik]

@datamweb not yet afaik