gcompris: fix private Qt6 targets search for Qt 6.10

fix https://hydra.nixos.org/build/311320100/log/tail
```
CMake Error at src/core/CMakeLists.txt:112 (target_link_libraries):
  Target "gcompris-qt" links to:

    Qt6::CorePrivate

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.
```

0 files changed, 0 insertions, 0 deletions