Update QuartzDataSourceInitializerTests.commentPrefixCanBeCustomized to use a custom prefix that isn't covered by the default

[wilkinsona]

The test uses ## as the custom prefix, but this is covered by the default of #. As a result the test passes without setting spring.quartz.jdbc.comment-prefix=##.

[adiohana]

@wilkinsona I created #18285 for this.
please let me know if that's what you meant.

[wilkinsona]

Closing in favour of #18285.