fix: make function async

lnbits/app.py

@@ -115,7 +115,7 @@ async def check_funding_source() -> None:
     )
 
 
-def check_installed_extensions():
+async def check_installed_extensions():
     """
     Check extensions that have been installed, but for some reason no longer present in the 'lnbits/extensions' directory.
     One reason might be a docker-container that was re-created.