modules: openthread: Switch to picolib

As requested by Zephyr SDK 1.0.0, picolib must be used.

Signed-off-by: Arkadiusz Balys <arkadiusz.balys@nordicsemi.no>

Author: ArekBalysNordic

subsys/net/openthread/Kconfig.defconfig

@@ -91,7 +91,7 @@ config OPENTHREAD_PING_SENDER
 	default y
 
 choice LIBC_IMPLEMENTATION
-	default NEWLIB_LIBC
+	default PICOLIBC
 endchoice
 
 config NEWLIB_LIBC_NANO