ESP32-C6: `board.UART()` on GPIO16 and GPIO17 is returning "Invalid pins"

ESP32-C6, at least: `board.UART()` or `busio.uART()` on GPIO16 and GPIO17 is returning "Invalid pins".

Discovered by a user in Discord. I'm debugging this: may have to do with HP vs LP UARTs and which pins work for each kind. Also found there is incomplete cleanup when the  `busio.UART()` constructor raise an exception.