False value in SIGNATURE item table

[hnj2]

The current RP2350 datasheet describes the SIGNATURE item (Section 5.9.2.4) as follows:

However, the boot/picobin.h header defines:

#define PICOBIN_BLOCK_ITEM_SIGNATURE                    _u(0x09)

The first byte of a SIGNATURE item in the documentation should therefore be 0x09 not 0x4b.