fix: Improve Any decode error (#712)

* 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

* update test

* update error message

* address review feedback

---------

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

google/api_core/protobuf_helpers.py

@@ -63,9 +63,7 @@ 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__
-            )
+            f"Could not convert `{any_pb.TypeName()}` with underlying type `google.protobuf.any_pb2.Any` to `{msg_pb.DESCRIPTOR.full_name}`"
         )
 
     # Done; return the message.

tests/unit/test_protobuf_helpers.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import pytest
+import re
 
 from google.api import http_pb2
 from google.api_core import protobuf_helpers
@@ -65,7 +66,12 @@ def test_from_any_pb_failure():
     in_message = any_pb2.Any()
     in_message.Pack(date_pb2.Date(year=1990))
 
-    with pytest.raises(TypeError):
+    with pytest.raises(
+        TypeError,
+        match=re.escape(
+            "Could not convert `google.type.Date` with underlying type `google.protobuf.any_pb2.Any` to `google.type.TimeOfDay`"
+        ),
+    ):
         protobuf_helpers.from_any_pb(timeofday_pb2.TimeOfDay, in_message)