test against matrix of MPL versions #50
Description
We should test against the latest patch version for each MPL major+minor version combination we support. For example, for the versions {3.9.0, 3.9.1, 3.10.0}, we'd test against 3.9.1 and 3.10.0. In practice conda will usually pull the latest version so we can express the matrix as 3.9, 3.10 and get good coverage.