Skip PackPhar test if phar.readonly = 1

[Naktibalda]

Overview

This pull request:

• [ ] Fixes a bug
• [ ] Adds a feature
• [ ] Breaks backwards compatibility
• [ ] Has tests that cover changes
• [ ] Adds or fixes documentation

Summary

I run tests on different version of PHP and PackPhar test failed because phar.readoly was set to '1'. So I though that it would be nice if this test was skipped when it can't be executed in specific environment.