Update qty-input.tpl

[panariga]

fix: Ensure provided input attributes take precedence over defaults

This commit modifies the Smarty template to prevent default input attributes (e.g., class, name, value) from duplicating attributes that are already defined in the $attributes array.

Previously, default attributes were appended after the loop that applied provided attributes, resulting in double values which is break HTML standart.

Now, conditional checks are used to only apply default attributes when the corresponding attribute is not already set in the $attributes array.

Questions	Answers
Description?	Please be specific when describing this change. What did you change? Why?
Type?	bug fix / improvement / new feature / refactor
BC breaks?	yes / no
Deprecations?	yes / no
Fixed ticket?	Fixes #{issue URL here}, Fixes #{another issue URL here}
Sponsor company	Your company or customer's name goes here (if applicable).
How to test?	Indicate how to verify that this change works as expected.

[ps-jarvis]

Hello @panariga!

This is your first pull request on hummingbird repository of the PrestaShop project.

Thank you, and welcome to this Open Source community!