fix(deps): allow cachetools 5.0 for python 3.7+ (#937)

* fix(deps): allow cachetools 5.0 for python 3.7+

Changes listed https://github.com/tkem/cachetools/blob/master/CHANGELOG.rst#v500-2021-12-21

* chore: remove split pin

* Update setup.py

* 🦉 Updates from OwlBot

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: arithmetic1728 <58957152+arithmetic1728@users.noreply.github.com>

Author: 3 people

setup.py

@@ -20,7 +20,7 @@
 
 
 DEPENDENCIES = (
-    "cachetools>=2.0.0,<5.0",
+    "cachetools>=2.0.0,<6.0",
     "pyasn1-modules>=0.2.1",
     # rsa==4.5 is the last version to support 2.7
     # https://github.com/sybrenstuvel/python-rsa/issues/152#issuecomment-643470233