Merge branch '3.4' into 4.2

* 3.4:
  Updates the tip explaining how to set the base phpunit version

components/phpunit_bridge.rst

@@ -403,7 +403,7 @@ different class, do it explicitly using ``ClockMock::register(MyClass::class)``:
 
     use App\MyClass;
     use PHPUnit\Framework\TestCase;
-    use Symfony\Bridge\PhpUnit\ClockMock; 
+    use Symfony\Bridge\PhpUnit\ClockMock;
 
     /**
      * @group time-sensitive
@@ -595,8 +595,13 @@ If you have installed the bridge through Composer, you can run it by calling e.g
 
 .. tip::
 
-    Set the ``SYMFONY_PHPUNIT_VERSION`` env var to e.g. ``5.5`` to change the
-    base version of PHPUnit to ``5.5`` instead of the default ``5.3``.
+    It's possible to change the base version of PHPUnit by setting the
+    ``SYMFONY_PHPUNIT_VERSION`` env var in the ``phpunit.xml.dist`` file (e.g.
+    ``<server name="SYMFONY_PHPUNIT_VERSION" value="5.5" />``). This is the
+    preferred method as it can be committed to your version control repository.
+
+    It's also possible to set ``SYMFONY_PHPUNIT_VERSION`` as a real env var
+    (not defined in a :doc:`dotenv </components/dotenv>` file).
 
     It's also possible to set this env var in the ``phpunit.xml.dist`` file.