15.0.0. affects including of own sitepackages

# Bug Report

* [ x] Can you reproduce the problem on TYPO3 v12.4 LTS

## Description
Docker/DDEV-Composer Installation (12.4.22)
With Ver. 15.0.0. I can't include my own Sitepackage Extension (Version: dev-main) anymore. (Not in list of "Available Items" in the "Include TypoScript sets" of the Root-Template. When I update another Project from 14.0.7 to 15.0.0. the same behaviour. My sitepackage Ext. which was included before will not be included anymore and doesn`t show off in the section mentioned above. My sitepackage-extension is correctly installed

## Steps to Reproduce

1. Install a local Sitepackage-Ext. with 15.0.0. installed
2. Try to include your sitepackage-ext into the root-template

### Expected behavior

Installation of or update to 15.0.0. shouldn't effect sitepackages

Reproduce the issue with a local sitepackage extension in a TYPO3 15.0.0 Docker/DDEV-Composer installation. Start at the Root-Template's "Include TypoScript sets" section and verify whether the installed extension appears under "Available Items"; done means the sitepackage can be included after installation or upgrade.

Written by the indexing model from the issue text.