updated PHPUnit configuration (added XSD, removed defaults, proper formatting)
minor #678 update PHPUnit configuration (add XSD, remove defaults, proper formatting) (craue)

This PR was merged into the 2.3 branch.

Discussion
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update PHPUnit configuration (add XSD, remove defaults, proper formatting)

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | --
| License       | MIT
| Doc PR        | --

See symfony/symfony#11344.

Commits
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324692e updated PHPUnit configuration (added XSD, removed defaults, proper formatting)