minor #16563 [Testing] Update testing.rst (devSf2)

This PR was submitted for the 6.0 branch but it was merged into the 4.4 branch instead.

Discussion
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[Testing] Update testing.rst

Add missing testing environment option to 'doctrine:fixtures:load' command.

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Commits
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72ec88b Update testing.rst

Author: javiereguiluz

testing.rst

@@ -406,7 +406,7 @@ Empty the database and reload *all* the fixture classes with:
 
 .. code-block:: terminal
 
-    $ php bin/console doctrine:fixtures:load
+    $ php bin/console --env=test doctrine:fixtures:load
 
 For more information, read the `DoctrineFixturesBundle documentation`_.