Update phpunit/phpunit requirement from ^5.0 to ^8.3

[dependabot-preview]

Updates the requirements on phpunit/phpunit to permit the latest version.

Changelog

Sourced from phpunit/phpunit's changelog.

8.3.0 - 2019-08-02

Added

• Implemented #3687: Introduce MockBuilder::addMethods() and MockBuilder::onlyMethods() as alternatives to MockBuilder::setMethods()
• Implemented #3741: Format class names as well as method names in TestDox output
• Implemented #3748: Add option to sort tests based on information from @small, @medium, and @large
• Added TestCase::getActualOutputForAssertion() as a wrapper for TestCase::getActualOutput() to prevent a test being marked as risky when it prints output and that output is not expected using TestCase::expectOutputString() or TestCase::expectOutputRegEx()

Changed

• Implemented #2015: Prefix all code bundled in PHAR distribution with random/unique namespace
• Implemented #3503: The error handler has been refactored to not rely on global state
• Implemented #3521: The @errorHandler annotation, which controlled a feature that was not documented and did not work correctly, does not have an effect anymore
• Implemented #3522: The TestCase::setUseErrorHandler() method, which controlled a feature that was not documented and did not work correctly, has been deprecated and does not have an effect anymore
• Implemented #3687: MockBuilder::setMethods() is now deprecated

Commits

• c515316 Prepare release
• 28ae8c3 Fix
• 8778421 Update ChangeLog
• 8e3d506 Do not leak Reflection exceptions
• 691d437 Rename variable
• e4c6387 Fix exception messages
• 20b0b21 Warn of non-existent methods in createPartialMock
• 5e04f91 Only allow new mock methods to configure once
• d618fa3 Add onlyMethods, addMethods + deprecate setMethods
• bbd09bb Add throws, change error message + add class name
• Additional commits viewable in compare view

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