minor #20756 Fix 20635 (curry684, javiereguiluz)

This PR was merged into the 6.4 branch.

Discussion
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Fix 20635

When I merged #20635, an error happened and I cannot fix it. So, this is a new PR that contains the same commit as the original PR (to keep `@curry684`'s original authorship).

Commits
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89950ee Minor tweak
efed8f8 Remove reference to Local PHP Security Checker

Author: javiereguiluz

setup.rst

@@ -249,9 +249,9 @@ workflows to make them fail when there are vulnerabilities.
 .. tip::
 
     In continuous integration services you can check security vulnerabilities
-    using a different stand-alone project called `Local PHP Security Checker`_.
-    This is the same project used internally by ``check:security`` but much
-    smaller in size than the entire Symfony CLI.
+    by running the ``composer audit`` command. This uses the same data internally
+    as ``check:security`` but does not require installing the entire Symfony CLI
+    during CI or on CI workers.
 
 Symfony LTS Versions
 --------------------
@@ -318,7 +318,6 @@ Learn More
 .. _`The Symfony Demo Application`: https://github.com/symfony/demo
 .. _`Symfony Flex`: https://github.com/symfony/flex
 .. _`PHP security advisories database`: https://github.com/FriendsOfPHP/security-advisories
-.. _`Local PHP Security Checker`: https://github.com/fabpot/local-php-security-checker
 .. _`Symfony releases`: https://symfony.com/releases
 .. _`Main recipe repository`: https://github.com/symfony/recipes
 .. _`Contrib recipe repository`: https://github.com/symfony/recipes-contrib