tools: Make time-zones more case-insensitive (#55288)

gpt-5.5 likes to call the `now` tool with upper-case "UTC", leading to
this error:

> Failed to receive tool input: tool input was not fully received


Release Notes:

- N/A
c499a95218Oleksiy Syvokon committed on 4/30/2026, 9:15:36 AM· committed by GitHubparent24f6248
1 file changedLine totals unavailable