Replace fromisoformat with explicit construction of datetime

Author: iarspider

repo_config.py

@@ -4,6 +4,17 @@
 from os.path import dirname, abspath
 import os
 
+try:
+    import datetime.timezone.utc as UTC
+except ImportError:
+    class UTC(datetime.tzinfo):
+        def utcoffset(self, dt):
+            return datetime.timedelta(0)
+        def tzname(self, dt):
+            return "UTC"
+        def dst(self, dt):
+            return datetime.timedelta(0)
+
 GH_TOKEN = os.getenv("GH_TOKEN_FILE", "~/.github-token")
 GH_TOKEN_READONLY = "~/.github-token-readonly"
 CONFIG_DIR = dirname(abspath(__file__))
@@ -16,4 +27,4 @@
 IGNORE_ISSUES = {
     GH_CMSSW_ORGANIZATION + "/" + GH_CMSSW_REPO: [12368],
 }
-LEGACY_CATEGORIES = {"upgrade": datetime.datetime.fromisoformat("2025-10-10T00:00:00+00:00")}
+LEGACY_CATEGORIES = {"upgrade": datetime.datetime(2025, 10, 10, 0, 0, tzinfo=UTC)}