save a reference to created tasks, to avoid tasks disappearing

[anio]

This change saves references for created tasks to avoid tasks disappearing.

Save a reference to the result of this function, to avoid a task disappearing mid-execution. The event loop only keeps weak references to tasks. A task that isn’t referenced elsewhere may get garbage collected at any time, even before it’s done.

python docs

Please review the link: https://textual.textualize.io/blog/2023/02/11/the-heisenbug-lurking-in-your-async-code/