Increment beta version number on PR

[Mark2000]

Describe your use case
Our RL repo, https://github.com/AVSLab/bsk_rl/, would like to be able to check for a specific develop version of Basilisk. The best approach would be to increment the beta version number (e.g. 2.2.1b4->2.2.1b5) each time a PR is merged into develop.

Describe alternatives solutions you've considered
Considered checking for git hashes in my repo, but there is not a clean way to do that through python and would require looking through the whole git tree to see if the required version is somewhere in the current branch. Version numbers seem more robust and easier to access.

Additional context
I put together a proof of context here: https://github.com/Mark2000/bump_test