Interchange 0.4.2 breaks SMIRNOFF template generator

[j-wags]

It looks like the well-intentioned convenience behavior added in openforcefield/openff-interchange#1133 has broken the SMIRNOFFTemplateGenerator.

(thanks @dotsdl for initially spotting this)

For folks getting this error on freshly made envs, you can get around this by downpinning to openff-interchange=0.4.1

[mattwthompson]

Ahh ... that's unfortunate. Sorry about that

[mikemhenry]

I think we can also relax the "don't support custom forces" -- A quick look at the code makes it seem like is a guard so we don't have users expecting a force they define to get atom types parameterized, but as long as we don't load the force in the dictionary then it should be okay (will need to check if we lose it on the round trip or something like that)

[mikemhenry]

Quick fix for the feedstock here: conda-forge/openmmforcefields-feedstock#21