use google-api-core branch fix-lro-no-result for prototyping

Author: parthea

noxfile.py

@@ -232,6 +232,10 @@ def showcase_library(
     # Install gapic-generator-python
     session.install("-e", ".")
 
+    # For prototyping purposes only.
+    # Remove once https://github.com/googleapis/python-api-core/pull/810 is released
+    session.install("google-api-core @ git+https://github.com/googleapis/python-api-core.git@fix-lro-no-result", "--ignore-installed")
+
     # Install grpcio-tools for protoc
     session.install("grpcio-tools")