Bump minimum version to run Friendica to PHP 7.4

- Update version filter of mobiledetect/mobiledetectlib and psr/container to PHP 7.4 versions
- Remove PHP 7.3 PHPUnit instance
- Remove PHP 7.2 specific PDO exception in tests

tests/functional/DependencyCheckTest.php

@@ -80,12 +80,6 @@ class DependencyCheckTest extends FixtureTest
 
 	public function testDatabase()
 	{
-		// PDO needs to be disabled for PHP 7.2, see https://jira.mariadb.org/browse/MDEV-24121
-		if (version_compare(PHP_VERSION, '7.3') < 0) {
-			$configCache = $this->dice->create(Cache::class);
-			$configCache->set('database', 'disable_pdo', true);
-		}
-
 		/** @var Database $database */
 		$database = $this->dice->create(Database::class);