Improve Any decoding-error.

Was:

TypeError: Could not convert Any to PredictLongRunningResponse

Now:

TypeError: Could not convert
   Any[google.ai.generativelanguage.v1main.PredictLongRunningResponse] to
       google.ai.generativelanguage.v1beta.PredictLongRunningResponse

google/api_core/protobuf_helpers.py

@@ -63,8 +63,8 @@ def from_any_pb(pb_type, any_pb):
     # Unpack the Any object and populate the protobuf message instance.
     if not any_pb.Unpack(msg_pb):
         raise TypeError(
-            "Could not convert {} to {}".format(
-                any_pb.__class__.__name__, pb_type.__name__
+            "Could not convert\n   Any[{}] to\n       {}".format(
+                any_pb.TypeName(), msg_pb.DESCRIPTOR.full_name
             )
         )