minor #10930 Fixed the "learn more" section of Testing article (javiereguiluz)

This PR was squashed before being merged into the 3.4 branch (closes #10930).

Discussion
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Fixed the "learn more" section of Testing article

Reported by @jmsche in Symfony's Slack. This is how it looks before this fix:

![testing-error](https://user-images.githubusercontent.com/73419/51758071-269d4d00-20c5-11e9-9439-096c89083fd4.png)

Commits
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e70893a Fixed the \"learn more\" section of Testing article

Author: javiereguiluz

testing.rst

@@ -973,11 +973,9 @@ Learn more
     :glob:
 
     testing/*
-
-* :ref:`Testing a console command <console-testing-commands>`
-* :doc:`The chapter about tests in the Symfony Framework Best Practices </best_practices/tests>`
-* :doc:`/components/dom_crawler`
-* :doc:`/components/css_selector`
+    /best_practices/tests
+    /components/dom_crawler
+    /components/css_selector
 
 .. _`PHPUnit`: https://phpunit.de/
 .. _`documentation`: https://phpunit.readthedocs.io/