MAINT: add compatibility with pymc_v5

Closes #658 (closed)

Hopefully, this MR will allow both pymc4 and pymc5 to work.

bilby/core/sampler/pymc.py

@@ -140,7 +140,7 @@ class Pymc(MCMCSampler):
             import aesara.tensor as tt
             from aesara.compile.ops import as_op  # noqa
 
-        return pytensor, tt, as_op
+        return tensor, tt, as_op
 
     def _verify_parameters(self):
         """