Use anyhow::Error in end-to-end tests (#1878)

* Import `anyhow::Result` in end-to-end tests

Reduce the visual noise a bit.

* Return `anyhow::Result<()>` from end-to-end tests

Prepare to use the try operator `?` inside the test functions.

* Replace `Result::unwrap` with try operator (`?`)

Reduce the code noise.