Upgrade to the latest version of Lombiq.Tests.UI (OCC-102)

[sarahelsaig]

Is your feature request related to a problem? Please describe

The version currently used runs the tested webapp as a separate process (harder to debug) whereas version 4.0.1 uses WebApplicationFactory to instantiate the webapp in the same process. This involves some breaking changes, so it's also necessary in case we will need additional features from the library in the future.

Describe the solution you'd like

• Upgrade version
• Make necessary changes according to migration docs here.
• Review updated OC testing docs here.

Jira issue

[DemeSzabolcs]

@DAud-IcI What do you think about migrating to the new .NET 6.0 hosting model, in this issue? We already use this in other projects (example: https://github.com/Lombiq/Open-Source-Orchard-Core-Extensions/blob/dev/src/Lombiq.OSOCE.Web/Program.cs). I have to do things in Program.cs anyway, so this could be a good opportunity. (It should be really easy)

[sarahelsaig]

I'm in favor of it.