Update required minimum jsonschema version >= 4.16.0

DeprecationWarnings for jsonschema has been fixed at below path.

https://review.opendev.org/c/openstack/tempest/+/875264

But it is required to update the minimum jsonschema version >= 4.16.0
for including a below commit.

https://github.com/python-jsonschema/jsonschema/commit/ee024ffc61bee56b25e816f489d7365fe1445c6d

Closes-Bug: #2008490
Change-Id: I0f459d7f74406e30af725c751f3b7cd1a6a931a6
diff --git a/requirements.txt b/requirements.txt
index 6e66046..932c64c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,7 +3,7 @@
 # process, which may cause wedges in the gate later.
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 cliff!=2.9.0,>=2.8.0 # Apache-2.0
-jsonschema>=3.2.0 # MIT
+jsonschema>=4.16.0 # MIT
 testtools>=2.2.0 # MIT
 paramiko>=2.7.0 # LGPLv2.1+
 cryptography>=2.1 # BSD/Apache-2.0