Handling updates where version is more complex

We have some cases like [this one]( https://github.com/conda-forge/pygit2-feedstock/pull/3/files/c3f4b22ef39ed1694e6066873b37e3715c4f2056#r172032340 ) where the version in Jinja ends up being a function of other Jinja variables. This is typically motivate by two things AFAIAA.

1. The URL is some more complex combination of version components.
2. The version is needed to pin its dependencies somehow.

These might be rare enough that the answer is we adjust the recipes so the bot can update them more easily. Figured I'd raise the issue anyways though to see if anyone had other ideas.