minor #21217 [Typo] Fixed typo in setup.rst (mnocon)

This PR was merged into the 6.4 branch.

Discussion
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[Typo] Fixed typo in setup.rst

Hi!

Just fixing a small typo I've noticed.

I plan to contribute more in the future, I hope this PR is just a start 😄

Best,
Marek

Commits
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547dac6 Fixed typo in setup.rst

Author: javiereguiluz

setup.rst

@@ -103,7 +103,7 @@ Git, setup your project with the following commands:
 
 You'll probably also need to customize your :ref:`.env file <config-dot-env>`
 and do a few other project-specific tasks (e.g. creating a database). When
-working on a existing Symfony application for the first time, it may be useful
+working on an existing Symfony application for the first time, it may be useful
 to run this command which displays information about the project:
 
 .. code-block:: terminal