minor #13122 [String] Fix quotes (OskarStark)

This PR was merged into the master branch.

Discussion
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[String] Fix quotes

Commits
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3d634fa [String] Fix quotes

Author: javiereguiluz

components/string.rst

@@ -121,7 +121,7 @@ to make your code more concise::
     use function Symfony\Component\String\s;
 
     // creates a ByteString object
-    $foo = s('\xfe\xff');
+    $foo = s("\xfe\xff");
     // creates a UnicodeString object
     $foo = s('अनुच्छेद');