[ical4j 4.x] Update `JtxCollection`/`JtxICalObject`

[rfc2822]

Update jtx Board access code so that it uses icalj 4.x instead of 3.x.

No functional changes.

• JtxContract
• JtxCollection
• JtxICalObject

[cketti]

Some tests in JtxICalObjectTest currently seem to be skipped, presumably due to GrantPermissionOrSkipRule. When working on this issue, please make sure this is fixed and those tests run when you test locally and also on CI.