fix ctypes test alignment assumptions (closes #20946)

Patch by Andreas Schwab.
merge 3.3 (#20946)
Issue #20950: Fix typo asyncio doc, wait() has no self parameter

self parameter is implicit. Mention also that communicate() and wait() are
coroutines.
improve set_tunnel docs (closes #11448)

Patch by Ryan Kelly, karl, and Nikolaus Rath.
merge 3.3 (#11448)