minor symfony#8977 Update the DSN format in XML, it should be escaped (pouyana, javiereguiluz)

This PR was merged into the 4.0 branch.

Discussion
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Update the DSN format in XML, it should be escaped

So using the same setting gives

```
Could not load "/var/www/app/phpunit.xml.dist".
EntityRef: expecting ';'
```

The DSN should be escaped before added in the XML file.

Commits
-------

a1486af Removed additional Doctrine config params
cbffec3 Update the DSN format in XML, it should be escaped

Author: javiereguiluz

testing/database.rst

@@ -121,7 +121,7 @@ To do this, you can override the value of the ``DATABASE_URL`` env var in the
     <phpunit>
         <php>
             <!-- the value is the Doctrine connection string in DSN format -->
-            <env name="DATABASE_URL" value="mysql://USERNAME:PASSWORD@127.0.0.1/DB_NAME?charset=utf8mb4&serverVersion=5.7" />
+            <env name="DATABASE_URL" value="mysql://USERNAME:PASSWORD@127.0.0.1/DB_NAME" />
         </php>
         <!-- ... -->
     </phpunit>