Update phpunit/phpunit requirement to ^6.5|^7.0

[dependabot-preview]

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

Changelog

Sourced from phpunit/phpunit's changelog.

Changes in PHPUnit 5.7

All notable changes of the PHPUnit 5.7 release series are documented in this file using the Keep a CHANGELOG principles.

[5.7.27] - 2018-02-01

Fixed

• Fixed #2236: Exceptions in tearDown() do not affect getStatus()
• Fixed #2950: Class extending PHPUnit\Framework\TestSuite does not extend PHPUnit\FrameworkTestCase
• Fixed #2972: PHPUnit crashes when test suite contains both .phpt files and unconventionally named tests

[5.7.26] - 2017-12-17

Fixed

• Fixed #2472: PHPUnit\Util\Getopt uses deprecated each() function
• Fixed #2833: Test class loaded during data provider execution is not discovered
• Fixed #2922: Test class is not discovered when there is a test class with [**group**](https://github.com/group) and provider throwing exception in it, tests are run with --exclude-group for that group, there is another class called later (after the class from above), and the name of that another class does not match its filename

[5.7.25] - 2017-11-14

Fixed

• Fixed #2859: Regression caused by fix for #2833

[5.7.24] - 2017-11-14

Fixed

• Fixed #2833: Test class loaded during data provider execution is not discovered

[5.7.23] - 2017-10-15

Fixed

• Fixed #2731: Empty exception message cannot be expected

[5.7.22] - 2017-09-24

Fixed

• Fixed #2769: Usage of setUseErrorHandler() produces Undefined variable error

[5.7.21] - 2017-06-21

Added

• Added PHPUnit\Framework\AssertionFailedError, PHPUnit\Framework\Test, and PHPUnit\Framework\TestSuite to the forward compatibility layer for PHPUnit 6

... (truncated)

Commits

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