Add ECMA-402 PR 788

CC @gibson042 

Added it with an hourglass.

2023/09.md

@@ -86,6 +86,8 @@ When applicable, use these emoji as a prefix to the agenda item topic.
     |   | 5m      | needs consensus:  [ecma402#758](https://github.com/tc39/ecma402/pull/758)  Normative: Change the hourCycle default logic | Ben Allen |
     |   | 10m     | needs consensus:  [ecma402#811](https://github.com/tc39/ecma402/pull/811)  Normative: Fix order of rounding* option reads and resolvedOptions() | Ben Allen |
     |   | 10m     | [Update GetSubstitution to match reality](https://github.com/tc39/ecma262/pull/3157) | Richard Gibson |
+    |   | 20m     | ⌛️ needs consensus:  [ecma402#788](https://github.com/tc39/ecma402/pull/788)  Normative: Allow UTC offset time zones | Ben Allen |
+
 1. Overflow from previous meeting
 
     | ✓ | timebox | topic | presenter |