Make scheduler timezone documentation consistent with javadoc

[zanmagerl]

All other configuration properties in scheduler documentation reference properties with $, and also javadoc uses it with $:

The value can be a property expression. In this case, the scheduler attempts to use the configured value instead:
  * {@code @Scheduled(timeZone = "${myJob.timeZone}")}. Additionally, the property expression can specify a default value:
  * {@code @Scheduled(timeZone = "${myJob.timeZone:Europe/Prague}")}.

This commit makes it consistent with other references.

[github-actions]

🙈 The PR is closed and the preview is expired.

[quarkus-bot]

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It should be safe to merge provided you have a look at the other checks in the summary.

[gsmet]

Good catch, thanks!