Acronyms with inner digits do not decamelize correctly

[lorrin]

decamelize treats a sequence of upper case characters followed by lowercase characters as two words, one being all but the last upper case character (presumably an acronym), the rest being the second word. humps.decamelize('AWSThing') yields 'aws_thing'. Acronyms may end in digits as well: humps.decamelize('B52Thing') yields 'b52_thing'. This logic is not correctly applied when the acronym contains inner digits.

To Reproduce

>>> humps.decamelize('B2BThing')
'b2_b_thing'

Expected behavior
All upper case characters and digits except the last one should be treated as a single word, yielding b2b_thing.

Additional context
pyhumps-3.5.3 on Python 3.10.2 on macOS 12.3.1 (21E258)