PHP 8.0: Fix all problems detected by phplint

Steps (for 311_STABLE and master) Ensure that you're using PHP 8.0 to run these tests Init phpunit ( php admin/tool/phpunit/cli/init.php ). Run vendor/bin/phpunit --testsuite core_phpunit_testsuite --testdox Verify that the test ends ok ( OK (XX tests, YYY assertions) ) (numbers don't matter). Verify that the output includes a group of tests with heading: phpunit_dataset_test (core\phpunit_dataset_test) Verify that the group includes a good number of tests, all them passing ok. Run vendor/bin/phpunit lib/phpunit/tests/phpunit_dataset_test.php Verify that the test ends ok OK (44 tests, 135 assertions) Run php -l lib/phpunit/tests/phpunit_dataset_test.php Verify that "No syntax errors detected..." is the result. Run php -l lib/horde/framework/Horde/Imap/Client/Exception/ServerResponse.php Verify that "No syntax errors detected..." is the result. Steps (for 310_STABLE) Ensure that you're using PHP 7.4 to run these tests Repeat all the steps (but number 1) executed for "311_STABLE and master" above.