fix: patches sometimes uninstall right after install (package:flutter_foreground_task)

[eseidel]

Two customers have reported a bad (occasional) interaction between Shorebird and some plugins which create a FlutterEngine, (but don't actually use it), causing Shorebird's launch tracking to get confused and think a patch crashed an uninstall it right away.

This only happens if the plugin (in this case, package:flutter_foreground_task) is invoked right between when a patch is installed before it it successfully launched from.

The bug is our fault. Our launch tracking gets confused by (surprising) behavior from the plugin which we need to fix.

@bryanoltman is working on a fix, which we hope to release later this week. Thanks!