Randomize testing user emails and passwords

[williamjallen]

The tests currently create users with a fixed email address and password, which can cause conflicts if multiple tests are running at the same time. See this failed test, for example. This PR resolves the issue by creating users with email addresses and passwords containing UUIDs.

Output from a test with conflicts for reference

PHPUnit 9.6.4 by Sebastian Bergmann and contributors.

E.                                                                  2 / 2 (100%)

Time: 00:00.206, Memory: 32.00 MB

There was 1 error:

1) Tests\Feature\Jobs\PruneAuthTokensTest::testExpiredAuthTokenDeleted
Illuminate\Database\UniqueConstraintViolationException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'jane@smith' for key 'user.user_email_unique' (Connection: mysql, SQL: insert into `user` (`firstname`, `lastname`, `email`, `password`, `institution`, `admin`, `updated_at`, `created_at`) values (Jane, Smith, jane@smith, 12345, me, 0, 2024-06-04 15:05:28, 2024-06-04 15:05:28))

/cdash/vendor/laravel/framework/src/Illuminate/Database/Connection.php:824
/cdash/vendor/laravel/framework/src/Illuminate/Database/Connection.php:783
/cdash/vendor/laravel/framework/src/Illuminate/Database/Connection.php:576
/cdash/vendor/laravel/framework/src/Illuminate/Database/Connection.php:540
/cdash/vendor/laravel/framework/src/Illuminate/Database/Query/Processors/Processor.php:32
/cdash/vendor/laravel/framework/src/Illuminate/Database/Query/Builder.php:3507
/cdash/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Builder.php:1982
/cdash/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1333
/cdash/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1298
/cdash/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1137
/cdash/tests/Traits/CreatesUsers.php:33
/cdash/tests/Feature/Jobs/PruneAuthTokensTest.php:23

Caused by
PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'jane@smith' for key 'user.user_email_unique'

/cdash/vendor/laravel/framework/src/Illuminate/Database/Connection.php:587
/cdash/vendor/laravel/framework/src/Illuminate/Database/Connection.php:816
/cdash/vendor/laravel/framework/src/Illuminate/Database/Connection.php:783
/cdash/vendor/laravel/framework/src/Illuminate/Database/Connection.php:576
/cdash/vendor/laravel/framework/src/Illuminate/Database/Connection.php:540
/cdash/vendor/laravel/framework/src/Illuminate/Database/Query/Processors/Processor.php:32
/cdash/vendor/laravel/framework/src/Illuminate/Database/Query/Builder.php:3507
/cdash/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Builder.php:1982
/cdash/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1333
/cdash/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1298
/cdash/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1137
/cdash/tests/Traits/CreatesUsers.php:33
/cdash/tests/Feature/Jobs/PruneAuthTokensTest.php:23

ERRORS!
Tests: 2, Assertions: 2, Errors: 1.