* Fix testDataDownload in CI
This test was downloading from https://www.example.com and https://www.iana.org but something funny seems to have happened to the JVM CA certificates on Github actions.
Pointing to a site we control, skip.dev, ensures that we'll be in charge of any weirdness in changing certificate authorities.
* Robustify TestURLSession `testGetTasks`
`testGetTasks` assumed that the task would remain pending long enough to `await session.allTasks` and then `await session.tasks`, but the task might fail or succeed faster than that.
I split the test into `testGetTasks` which only tests `session.tasks`, and `testGetAllTasks` which only tests `session.allTasks`, minimizing the likelihood of race conditions.
* Robustify TestURLSession `testFinishTasksAndInvalidate`
Poll for success in a loop for up to two seconds before failing
