Support PHPUnit 10

[herndlm]

fyi I wanted to open a PR, but most likely to properly test it also prophecy (dev dep from this package) needs to get PHPUnit 10 support first. Looks like they're already working on it via phpspec/prophecy#585

[michalbundyra]

@herndlm thanks, I've seen it already, was thinking about dropping prophecy here, there are going to be more issues in general here, so I am even tempted to support only PHPUnit 10 (or 9 and 10) in next minor release to clean up this package a bit. It's horrible mess atm.

[michalbundyra]

@herndlm instead of waiting for prophecy to get PHPUnit 10 support I've tried with mockery as the second mocking library in our tests - and it seems to be successful. PHPUnit 10 support has been provided in PR #56 and just released in 2.7.0.

Any feedback appreciated!