Using `ParentInjectorPromise.all()` (which is a static method inherited
from `SyncPromise`) causes Closure Compiler (or some related tool) to
complain:
```
TypeError: ...$packages$upgrade$src$common$src$downgrade_component_ParentInjectorPromise.all is not a function
```
Switching to `SyncPromise.all()` (the static method on the parent class)
to avoid this error.
PR Close#31986