The `cron` package uses `timeZone`, while Sentry internally uses
`timezone`. This caused Sentry cron jobs to be incorrectly upserted with
no time zone information. Because of the use of the `...(timeZone ? {
timeZone } : undefined)` idiom, TypeScript type checking did not catch
the mistake.

I kept `cron`'s `timeZone` capitalization within Sentry's
instrumentation and changed from the `...(timeZone ? { timeZone } :
undefined)` idiom so TypeScript could catch mistakes of this sort.
(Passing an undefined `timezone` appears to be okay, because Sentry's
`node-cron` instrumentation does it.)