[NFC] Update PHPUnit config to not cache results in phpunit8 and add …

[seamuslee001]

…more voids into PayflowProTest

Overview

Title says it all

Before

Tests results cached in phpunit8

After

No caching of tests results in phpunit8

ping @eileenmcnaughton

[civibot]

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[eileenmcnaughton]

@seamuslee001 do you have a good link to the meaning of the new option? (I can google but wondered if you had found one that is 'good')

[seamuslee001]

@eileenmcnaughton https://stackoverflow.com/questions/55091768/what-is-phpunit-result-cache

[eileenmcnaughton]

@seamuslee001 that seems OK - there are some follow ups to civix we probably need to do and also to add the .phpunit.result.cache to gitignore so people don't add it by mistake - since they could run it differently locally

However, I don't think those are blocking on merging this