Dependencies: Relax version constraint on `pendulum`

[amotl]

Dear Michael,

thanks a stack for conceiving and maintaining arbitrary-dateparser, we are using it in Aika.

While upgrading to Python 3.12, we encountered some obstacles, where it would have been easier to use a more recent version of pendulum, for example the most recent 2.x release, version 2.1.2. However, this is not possible, because arbitrary-dateparser nails it down to the patch level.

arbitrary-dateparser/setup.py

Lines 18 to 20 in e8c6085

	install_requires=[
	'pendulum==2.0.5',
	],

Would you accept a corresponding patch to relax the version constraint?

With kind regards,
Andreas.