revert back to libgrpc 1.73

Signed-off-by: Lonnie Liu <lonnie@anyscale.com>

Author: aslonnie

.ci_support/linux_64_python3.10.____cpython.yaml

@@ -21,7 +21,7 @@ docker_image:
 github_actions_labels:
 - cirun-openstack-cpu-4xlarge
 libgrpc:
-- '1.71'
+- '1.73'
 pin_run_as_build:
   python:
     min_pin: x.x