fix: tests expect task response

[equinor-ruaj]

Issue

Closes #262

Description

Sumo-core was updated to handle case deletes as a Task: https://github.com/equinor/sumo-core/pull/994
Update the tests to expect the new response.

• Do not try to convert to json
• Assert response text is "Accepted."

How to test

Run the two tests that were failing test_upload_duplicate_ensemble and test_upload_search_delete_ensemble_child and see that they pass.

(The tests are also run as part of the PR checks here)

Checklist

• No redundant `print()` statements, commented-out code, or other remnants from the development 👀
• New/refactored code is following same conventions as the rest of the code base 🧬
• New/refactored code is tested ⚙
• Documentation has been updated 🧾
• Commits are semantic ✅