Unused prior in Bayesian AB testing case study

Notebook title: What is A/B testing?
Notebook url: https://github.com/pymc-devs/pymc-examples/blob/main/examples/case_studies/bayesian_ab_testing.ipynb

Issue description

In the RevenueModel class the converted object goes unused:

converted = pm.Binomial(
                "converted", n=visitors, p=theta, observed=purchased, shape=num_variants
            )
revenue = pm.Gamma(
                "revenue", alpha=purchased, beta=lam, observed=total_revenue, shape=num_variants
            )

The following line uses purchased (which is supposed to represent collected data) as alpha - I'm guessing that should be converted?

Expected output

I'm a beginner Bayesian, so I'm not sure if the output is unexpected or not.

Proposed solution

In a local copy of the code, I replaced purchased with converted + 1e-8 (plus a small epsilon) in the revenue prior, and the code ran pretty much the same as before.

Open examples/case_studies/bayesian_ab_testing.ipynb and locate the RevenueModel class. Inspect how converted, purchased, and total_revenue are used, then run the notebook to compare the current behavior with any change. Done means resolving the unused converted object or documenting why the current revenue prior is correct, with the notebook still running successfully.