Issue #3460689: Unkown method writeWebConfig fix.

src/Service/KeyGeneratorService.php

@@ -73,7 +73,12 @@ class KeyGeneratorService {
     $this->validator->validateNotFilePublicPath([$dir_path]);
 
     FileSecurity::writeHtaccess($dir_path);
-    FileSecurity::writeWebConfig($dir_path);
+    // As writeWebConfig method is deprecated and removed from D11.
+    // Also drupal dropped IIS support which require web.config so its ideal
+    // to have a check and handle the backward compatibility.
+    if (method_exists(FileSecurity::class, 'writeWebConfig')) {
+      FileSecurity::writeWebConfig($dir_path);
+    }
 
     // Create Keys array.
     $keys = KeyGenerator::generateKeys();