TypeCombinatorTest: turn return into yield

[staabm]

I used rector to transform the test. I think its way more readable to have a single yield per test-case instead of a huge return [[], [], []] in which its hard to see where test-data from one test starts and where the next one starts etc.

just did the transformation on a single test for now, to discuss the overall idea.

this PR did not transform the yield from [[], [], []] into yield, as this is not yet implemented in rector.

wdyt?

[phpstan-bot]

This pull request has been marked as ready for review.

[staabm]

please do not merge yet, as I need to tripple check the results first. I was just asking for the idea at first

[ondrejmirtes]

I'm thinking:

1. I don't want to merge this before we merge and test and release the new PHPUnit rule. I want to see what it does with the current test suite as it has existed for years.
2. I want to eventually do this but with a custom rule here in phpstan-src that uses fixNode() to do this. I don't want to do it once with Rector and then get it wrong again, I want to continuously test it.