minor symfony#9258 Fix: Typo (localheinz)

This PR was merged into the 4.0 branch.

Discussion
----------

Fix: Typo

This PR

* [x] fixes a small typo

💁‍♂️ Running

```
$ git grep -i diferent
```

on [`4.0`](https://github.com/symfony/symfony-docs/tree/4.0) yields

```
testing/database.rst:116:``phpunit.xml.dist`` to use a diferent database for your tests:
```

Commits
-------

18b31b8 Fix: Typo

Author: javiereguiluz

testing/database.rst

@@ -113,7 +113,7 @@ not to overwrite data you entered when developing the application and also
 to be able to clear the database before every test.
 
 To do this, you can override the value of the ``DATABASE_URL`` env var in the
-``phpunit.xml.dist`` to use a diferent database for your tests:
+``phpunit.xml.dist`` to use a different database for your tests:
 
 .. code-block:: xml