chore: Use intersection types feature

[tienvx]

When running static code analysis on tests/, there will be a lot of errors like this:

Call to an undefined method PhpPact\SomeInterface|PHPUnit\Framework\MockObject\MockObject::expects().

This can be fixed by using intersection types instead of union types. This is a new feature from PHP 8.1 (lowest supported PHP version by Pact-PHP)

By doing this fix more than 110 errors (out of 218 errors) in #564