[BUGFIX] Handle missing $_SERVER['PATH_INFO']

Fix PHP8 warning issue if $_SERVER['PATH_INFO'] is not set.

Resolves: #96373
Releases: main, 11.4
Change-Id: I427aee39c6f6389e418f27474c01cbfd973355e1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72687
Reviewed-by: Helmut Hummel <typo3@helhum.io>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Helmut Hummel <typo3@helhum.io>

typo3/sysext/core/Classes/Utility/GeneralUtility.php

@@ -2506,7 +2506,7 @@ public static function getIndpEnv($getEnvName)
                 // return FALSE for CGI-versions, but that is only as long as SCRIPT_NAME is set equal to PATH_INFO
                 // because of PHP_SAPI=='cgi' (see above)
                 if (!Environment::isRunningOnCgiServer()) {
-                    $retVal = $_SERVER['PATH_INFO'];
+                    $retVal = $_SERVER['PATH_INFO'] ?? '';
                 }
                 break;
             case 'TYPO3_REV_PROXY':