AVR-LibC 2.3.1 released

[Georg-Johann Lay via Discussion of avr-libc development]

AVR-LibC 2.3.1 has just been released.

https://github.com/avrdudes/avr-libc/releases/tag/avr-libc-2_3_1-release
NEWS: 
https://github.com/avrdudes/avr-libc/blob/avr-libc-2_3/NEWS.md#changes-in-avr-libc-v231

It is a quick followup on 2.3.0 with two regression fixes.

AVR-LibC 2.3.0 has been released in December with too many changes to
mention all of them individually.

https://github.com/avrdudes/avr-libc/releases/tag/avr-libc-2_3_0-release
NEWS: 
https://github.com/avrdudes/avr-libc/blob/main/NEWS.md#changes-in-avr-libc-v230