fix: add cryptography to constraints file

Author: parthea

gapic/templates/testing/_default_constraints.j2

@@ -6,6 +6,8 @@ google-auth
 grpcio
 proto-plus
 protobuf
+# cryptography is a direct dependency of google-auth
+cryptography
 {% 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 %}

gapic/templates/testing/constraints-3.7.txt.j2

@@ -7,6 +7,8 @@
 # Then this file should have google-cloud-foo==1.14.0
 google-api-core==1.34.1
 google-auth==2.14.1
+# cryptography is a direct dependency of google-auth
+cryptography==38.0.3
 # TODO(https://github.com/googleapis/gapic-generator-python/issues/2453)
 # Add the minimum supported version of grpcio to constraints files
 proto-plus==1.22.3