channels.release() throws on attached channels instead of detaching (RTS4a)

[paddybyers]

Spec point

• RTS4a: "Detaches the channel and then releases the channel resource i.e. it's deleted and can then be garbage collected."

Observed behaviour

`channels.release()` throws error 90001 ("Channel operation failed as channel state is attached") when called on an attached channel, instead of detaching first and then releasing.

Test

This deviation is documented in the Realtime UTS test suite. The adapted test asserts the throw with code 90001 instead of successful detach-then-release.

Note: This deviation is from the Realtime test suite (not REST), so there is no `RUN_DEVIATIONS` reproduction command in the current REST PR. The test is documented in `test/uts/deviations.md`.

From PR #2191, branch `uts-rest`.

┆Issue is synchronized with this Jira Task by Unito

[SimonWoolf]

already fixed by 861bdc7