Product attribute fixtures improvements

[Zales0123]

Q	A
Branch?	1.3
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Related tickets	fixes #9252
License	MIT

There was an issue with product attribute fixtures, that there was no possibility to use more sophisticated attributes in product fixtures (like select or datetime). I decided to create a functional PHPUnit test for this bugfix, as Behat scenario would be a little bit strange and too technical, in my opinion.

[lchrusciel]

But huge 👏 for resolving bug itself ;)

[pamil]

The base of this pull-request was changed, you need fetch and reset your local branch
if you want to add new commits to this pull request. Reset before you pull, else commits
may become messed-up.

Unless you added new commits (to this branch) locally that you did not push yet,
execute git fetch origin && git reset "product-attribute-fixtures-improvements" to update your local branch.

Feel free to ask for assistance when you get stuck 👍

[pamil]

The base of this pull-request was changed, you need fetch and reset your local branch
if you want to add new commits to this pull request. Reset before you pull, else commits
may become messed-up.

Unless you added new commits (to this branch) locally that you did not push yet,
execute git fetch origin && git reset "product-attribute-fixtures-improvements" to update your local branch.

Feel free to ask for assistance when you get stuck 👍

[pamil]

Thank you, Mateusz! 🎉