Timezone data regresses after upgrade

A deploy bumps one direct dependency (api-client 2.10 to 2.11) for an unrelated bugfix; tests pass. Two days later, support reports that calendar events and reminders for users in a handful of regions (e.g., parts of Brazil, Egypt) fire one hour wrong, but only for dates after a recent government DST-rule change. Dashboards: no error rate change, no latency change; the only red signal is a user-reported 'reminder accuracy' business metric, regional. Other regions are fine. Context: api-client 2.11 tightened a transitive dependency pin and, as a side effect, pulled in an OLDER bundled timezone database (tzdata) than the previous transitive resolution had. Triage and mitigate.