Werk #15456: mailbox: Fix exchangelib warning in the service summary

Component	Checks & agents
Title	mailbox: Fix exchangelib warning in the service summary
Date	Mar 10, 2023
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.3.0b1 Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Ultimate MT 2.2.0b1 Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Ultimate MT 2.1.0p25 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT

Previously, a warning "WARNING:exchangelib.account:Failed to guess local timezone. Fallback to UTC" was shown in the mailbox service summary on some of the Checkmk servers.

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