fixed bug when using the CRON_TZ= cron expression

[jonnochoo]

Related to #706, when using the CRON_Z in an expression

CRON_TZ=Asia/Tokyo 0 6 * * *

The /dags page doesn't load, see below

The fixed version

[yohamta]

Looking great! Thank you for the amazing fix!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.97%. Comparing base (8dc577e) to head (a2cc200).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #707   +/-   ##
=======================================
  Coverage   61.97%   61.97%           
=======================================
  Files          53       53           
  Lines        5228     5228           
=======================================
  Hits         3240     3240           
  Misses       1734     1734           
  Partials      254      254           

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