[Quarkus 1.6][iCal] TimeZone-less DTSTART and DTEND changed to GMT in native mode

[ppalaga]

Probably caused by quarkusio/quarkus#5016

As a result, only zoned DTSTART and DTEND work properly.

[ppalaga]

This was definitely caused by the fact that with pre-20.1.0 GraalVM versions, the native image inherited the default time zone from the build environment. The GMT time zone seemed to be set by the Quarkus docker container (currently using GraalVM 19.3.1).

When testing with GraalVM 20.1.0 the issue does not occur anymore. From 20.1.0 release notes:

Improved support for timezones: information about all timezones is now included in every image, and the default timezone is correctly initialized at image startup and no longer fixed at image generation time.

The Quarkus builder image was upgraded to 20.1.0 recently, so the quirks in https://github.com/apache/camel-quarkus/blob/master/integration-tests/dataformat/src/main/java/org/apache/camel/quarkus/component/dataformat/it/ICalUtils.java#L87-L90 can be removed after the upgrade to Quarkus 1.6