Clearly indicate what is counted as a branch (#11423)
## Summary
As discussed in issue #11408, PLR0912 has a broader definition of
"branches" than I expected. This updates the documentation to include
this definition.
I also updated the example to include several different types of
branches, while still maintaining dictionary lookup as an alternative
solution. (Crafting a realistic example was quite a challenge 😅).
Closes https://github.com/astral-sh/ruff/issues/11408.
