CI workaround for PHP < 7.4 & MySQL 8

The error on PHP 7.2 & 7.3 is:

> PDO::__construct(): The server requested authentication method unknown to the client [caching_sha2_password]

See:
- https://stackoverflow.com/q/53066962/569101
- https://stackoverflow.com/q/52364415/569101
- https://stackoverflow.com/q/51489616/569101
- https://stackoverflow.com/q/50026939/569101

Also upgrade `actions/checkout` v3

app/config/tests/parameters_test.mysql.yml

@@ -1,6 +1,6 @@
 parameters:
     test_database_driver: pdo_mysql
-    test_database_host: localhost
+    test_database_host: 127.0.0.1
     test_database_port: 3306
     test_database_name: wallabag_test
     test_database_user: root