The issue has always been there, you just never noticed it because of no warning.
Actually, the issue was never there, because it was never an issue.
![Tongue :P](https://www.sfml-dev.org/forums/Smileys/default/tongue.gif)
The warning isn't supposed to apply in this case (extension supported under different name), and that's the current bug.
Just ignore the warning for now. The 2.3 release is a bit broken, but the patch release will be out shortly. If you absolutely need something functioning right now, you can stick to 2.2 for the time being.