fix: add AbstractFileUpload to composer-require-checker whitelist

AbstractFileUpload is used in FileUploadFactoryInterface return types
but is an optional dependency. Adding it to the whitelist allows
the optional file upload functionality to work correctly.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: koriym

composer-require-checker.json

@@ -1,7 +1,8 @@
 {
     "symbol-whitelist" : [
         "Koriym\\FileUpload\\FileUpload",
-        "Koriym\\FileUpload\\ErrorFileUpload"
+        "Koriym\\FileUpload\\ErrorFileUpload",
+        "Koriym\\FileUpload\\AbstractFileUpload"
     ],
     "php-core-extensions" : [
         "Core",