Simplify matching named timezones in HTTP header

src/lib/utils.py

@@ -64,10 +64,10 @@ def parse_date_header(date_str):
 
     In addition to standard(ish) formats, non-standard formats where the
     timezone is a named zone rather than an offset are detected and handled."""
-    list_zones = list(zoneinfo.available_timezones())
-    invalid_zones = [e for e in list_zones if e not in ("GMT", "UTC")]
-    if any((match_tz := tz) in date_str for tz in invalid_zones):
-        date_str_notz = date_str.replace(match_tz, "").strip()
+    for tz in zoneinfo.available_timezones():
+        if tz in ("UTC", "GMT") or not date_str.endswith(tz):
+            continue
+        date_str_notz = date_str[-(len(tz) + 1):]
         for date_fmt in [
             "%a, %d %b %Y %H:%M:%S",
             "%a, %d-%b-%Y %H:%M:%S",