refactor: fix phpstan errors in ResponseTrait

[paulbalandan]

Description
Fix errors in ResponseTrait.

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]

Fix errors in ResponseTrait.

Would it be possible to include the error link in the PR description?

[paulbalandan]

Would it be possible to include the error link in the PR description?

I'm not sure how to effectively do that as there's 70 fixed phpstan errors, and the errors themselves can be seen in the deleted lines in the baselines.

[datamweb]

Oh, I see — I thought those errors were already present in the GitHub Actions. I actually meant the link to the Actions runs.