fix: misc minor fixes in tests
- fix(019_01_05): set Accept header to JSON-LD as expected payload is JSON-LD
- fix(023_01_01): name is no longer part of core context (so can't be compacted if no context provided)
- fix(026_01): conform expectations to clause 5.7.8 (details of available attributes)
- fix: typo in comparison_result variable name
- fix: a list of one single string element is rendered as a string due to how JSON-LD expansion works
- fix(subscriptions): rename timeinterval to timeInterval