Update phpunit/phpunit from 7.5.16 to 7.5.18

[violinist-bot]

If you have a high test coverage index, and your tests for this pull request are passing, it should be both safe and recommended to merge this update.

Here is a list of changes between the version you use, and the version this pull request updates to:

• fcf6c4bfa Prepare release
• 29025600e Update ChangeLog
• 773be5e30 Ignore .psalm directory on PHPUnit 7.5 branch
• afb88b426 Adding fix
• d9d7efa23 Updating the test with expected behaviour
• ca4411e43 Add test for running tests in child process which are calling "exit"
• 81b7b0e5f Closes #3967
• 6ef9ac810 Fix: Build for any push or pull request
• a1137f15b Update tools
• 677e1ae62 HTTP -> HTTPS
• ac81488a8 Update tools
• d2666181b Update tools
• 909e50ab1 Fix: Reduce number of builds
• 1e0e83b7b Suppress PhpStorm rule: we cannot use a strict comparison here
• 2cfc3c896 Fix: Use hash of composer.json instead of commit hash for cache key
• 1bce3c96d Fix: Ignore codecov failures for now
• 69dc6274f Fix: Combine steps related to uploading code coverage
• c05f7cca1 Enhancement: Cache dependencies installed with composer between builds
• 8d0c2c132 Update tools
• fdc3245bc Update tools
• f9d9c8e2a Fix: Do not fail step when sending code coverage failed
• d0dcee9c1 Enhancement: Use stages so we can name the job
• 2c0c4f1ce Enhancement: Collect coverage for pull requests using Travis CI
• b2c4101e0 Enhancement: Run tests using GitHub actions
• 4c92a1529 Prepare release
• 6d01bd074 Update ChangeLog
• d703dcb5b Count Constaint - check \Countable first
• 24976a8d0 Prevent undefined stdout index error - #3727
• 2d33f54c1 Enhancement: Add test for execution with --version option
• 62b52dd2d Add early exit and simplify condition
• ea510c5e2 Use finally insead of isset on error
• 7be53b7ec Let Git know that tools/* are binary files
• d1e83a7ef Enhancement: Keep settings sorted
• bec7a7cd9 Enhancement: Keep unsupported sections sorted by name

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