minor symfony#51060 Fix htaccess sample to use index.php instead of app.php (Christopher Hertel)

This PR was merged into the 5.4 branch.

Discussion
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Fix htaccess sample to use index.php instead of app.php

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| License       | MIT
| Doc PR        | n/a

Kinda embarrassed that i found that thing ...

Commits
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2787e50 Fix htaccess sample to use index.php instead of app.php

Author: nicolas-grekas

src/Symfony/Component/HttpFoundation/ServerBag.php

@@ -51,7 +51,7 @@ public function getHeaders()
              * RewriteCond %{HTTP:Authorization} .+
              * RewriteRule ^ - [E=HTTP_AUTHORIZATION:%0]
              * RewriteCond %{REQUEST_FILENAME} !-f
-             * RewriteRule ^(.*)$ app.php [QSA,L]
+             * RewriteRule ^(.*)$ index.php [QSA,L]
              */
 
             $authorizationHeader = null;