Remove iso8601

As of python 3.11, the stdlib datetime.fromisoformat supports all of
the iso formats out there. We were just using this lib to parse
inbound github strings, so we should be able to drop this.

Change-Id: Iff684dc1701298cd5ba760c8059a901ed0c5d522

requirements.txt

@@ -25,7 +25,6 @@ cryptography>=39.0.0
 cachecontrol<0.12.7
 cachetools
 pyjwt>=2.5.0
-iso8601
 psutil
 google-re2>=1.1
 paho-mqtt<2.0.0

zuul/driver/github/githubconnection.py

@@ -34,7 +34,6 @@ import cachecontrol
 from cachecontrol.cache import DictCache
 from cachecontrol.heuristics import BaseHeuristic
 import cachetools
-import iso8601
 import jwt
 import requests
 import github3
@@ -1194,7 +1193,7 @@ class GithubClientManager:
 
             data = response.json()
 
-            expiry = iso8601.parse_date(data['expires_at'])
+            expiry = datetime.datetime.fromisoformat(data['expires_at'])
             token = data['token']
 
             self.installation_token_cache[installation_id] = (token, expiry)