.NET: Test methods should not use blocking task operations

[amotl]

There are a few admonitions on PRs related to .NET/C#.

Test methods should not use blocking task operations, as they can cause deadlocks. Use an async test method and await instead. (https://xunit.net/xunit.analyzers/rules/xUnit1031)

-- https://github.com/crate/cratedb-examples/pull/111/files, see section "Unchanged files with check annotations".

[amotl]

Currently, there seem to be other admonitions, only .NET/C# submits them the PR.

While it does not look that much important, it is important to reduce regular reporting and notification noise on this repository, and to take care of those details rigidly, so that significant signals received from this repository stand out, and will bring their value in notifying us early about any havocs which may have been introduced to the software components tested here in one way or another.