dillon1000/react

[Internal API only] Delete non-awaited form of act (#26339)

**This commit only affects the internal version of `act` that we use in
this repo. The public `act` API is unaffected, for now.**

We should always await the result of an `act` call so that any work
queued in a microtask has a chance to flush. Neglecting to do this can
cause us to miss bugs when testing React behavior.

I codemodded all the existing `act` callers in previous PRs.