tests: ensure tests run with protobuf 7.x

Author: parthea

gapic/templates/testing/constraints-3.14.txt.j2

@@ -10,7 +10,7 @@ google-api-core>=2
 google-auth>=2
 grpcio>=1
 proto-plus>=1
-protobuf>=6
+protobuf>=7
 {% for package_tuple, package_info in pypi_packages.items() %}
 {# Quick check to make sure `package_info.package_name` is not the package being generated so we don't circularly include this package in its own constraints file. #}
 {% if api.naming.warehouse_package_name != package_info.package_name %}