test(testutils): Update testing constraints to 3.10 and drop 3.9

Author: chalmerlowe

packages/google-cloud-testutils/testing/constraints-3.10.txt

@@ -0,0 +1,10 @@
+# This constraints file is used to check that lower bounds
+# are correct in setup.py
+# List *all* library dependencies and extras in this file.
+# Pin the version to the lower bound.
+#
+# e.g., if setup.py has "foo >= 1.14.0, < 2.0.0dev",
+# Then this file should have foo==1.14.0
+click==7.0.0
+google-auth==0.4.0
+packaging==22.0