Bring Espaloma tests back online

[mattwthompson]

  error    libmamba Could not solve for environment specs
      The following packages are incompatible
      └─ espaloma >=0.3.1  is not installable because there are no viable options
         ├─ espaloma 0.3.1 would require
         │  └─ openmmforcefields >=0.11.2  with the potential options
         │     ├─ openmmforcefields [0.11.2|0.12.0] would require
         │     │  └─ ambertools >=20.0,<23 , which does not exist (perhaps a missing channel);
         │     └─ openmmforcefields 0.13.0 would require
         │        └─ espaloma >=0.3.2 , which can be installed;
         └─ espaloma 0.3.2 would require
            └─ dgl 1.1.2.* , which does not exist (perhaps a missing channel).
  critical libmamba Could not solve for environment specs

Originally posted by @mattwthompson in #334 (comment)