Update phpunit to 9.5.19

[pavog]

If you use php-lock in an environment with php >= 8.0, you will get the following error when running composer install:

Installing dependencies from lock file (including require-dev)
Verifying lock file contents can be installed on current platform.
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. It is recommended that you run `composer update` or `composer update <package name>`.
Your lock file does not contain a compatible set of packages. Please run composer update.

  Problem 1
    - phpspec/prophecy is locked to version 1.11.1 and an update of this package was not requested.
    - phpspec/prophecy 1.11.1 requires php ^7.2 -> your php version (8.1.3) does not satisfy that requirement.
  Problem 2
    - phpspec/prophecy 1.11.1 requires php ^7.2 -> your php version (8.1.3) does not satisfy that requirement.
    - phpunit/phpunit 9.3.9 requires phpspec/prophecy ^1.11.1 -> satisfiable by phpspec/prophecy[1.11.1].
    - phpunit/phpunit is locked to version 9.3.9 and an update of this package was not requested.

This happens because phpunit 9.3.* requires phpspec/prophecy ^1.11.1, which does not allow php 8.
phpspec/prophecy 1.12 allows php 8.
We need at least phpunit 9.4.1 to use phpspec/prophecy ^1.12.1.