minor #9822 Fixed a RST syntax issue (javiereguiluz)

This PR was merged into the 4.0 branch.

Discussion
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Fixed a RST syntax issue

As seen on https://symfony.com/doc/current/testing.html

Commits
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0dcd453 Fixed a RST syntax issue

Author: javiereguiluz

testing.rst

@@ -271,9 +271,9 @@ document::
     Instead of installing each testing dependency individually, you can use the
     Symfony Test pack to install all those dependencies at once:
 
-        .. code-block:: terminal
+    .. code-block:: terminal
 
-            $ composer require --dev symfony/test-pack
+        $ composer require --dev symfony/test-pack
 
 .. index::
    single: Tests; Assertions