Update phpunit/phpunit requirement from ^7.0 to ^7.0 || ^9.0

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

Changelog

Sourced from phpunit/phpunit's changelog.

9.4.2 - 2020-10-19

Added

• Added missing PHPUnit\Framework\assertObjectEquals() and PHPUnit\Framework\objectEquals() wrapper functions

Changed

• PHPUnit\Framework\Assert::assertObjectEquals() is now static

9.4.1 - 2020-10-11

Fixed

• #4480: Methods with "static" return type (introduced in PHP 8) are not handled correctly by test double code generator

9.4.0 - 2020-10-02

Added

• #4462: Support for Cobertura XML report format
• #4464: Filter based on covered (@covers) / used (@uses) units of code
• #4467: Convenient custom comparison of objects

Changed

• The PHPUnit XML configuration generator (that is invoked using the --generate-configuration CLI option) now asks for a cache directory (default: .phpunit.cache)

Commits

• 3866b2e Prepare release
• 8f081a9 Add missing wrapper functions
• 53e1c2c Add missing static declaration
• 20c6850 Fix hasRandomOrderSeer -> hasRandomOrderSeed typo
• 74af26c Merge branch '8.5' into 9.4
• adee671 Update tools
• 1f09a12 Prepare release
• 609d52d Closes #4480
• 0a0ac90 Inline object
• 7646ea0 Bump
• Additional commits viewable in compare view

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