[MatStepper] FormControlLike is not compatible with FormGroup

What is the expected behavior?

The stepControl attribute of the CdkStep/MatStep classes should be castable to/assignable from a FormGroup or FormArray.

What is the current behavior?

Conversion of type 'FormControlLike' to type 'FormGroup' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first. Property 'controls' is missing in type 'FormControlLike'.
Happens during compilation when trying to cast FormControlLike to a FormGroup.

Type FormGroup is not assignable to type FormControlLike
Is the warning shown in HTML files when trying to assign a FormGroup to the stepControl input of a MatStep.

What are the steps to reproduce?

Create a MatStepper with a FormGroup assigned to a stepControl of one of the MatSteps. To reproduce the compilation issue, try to cast the stepControl of one step into a FormGroup within a TypeScript function.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Material Version 7.3.7

Reproduce the compilation issue with Angular Material 7.3.7 and TypeScript using a MatStepper whose MatStep stepControl is a FormGroup. Inspect the CdkStep/MatStep stepControl typing first; done means FormGroup and FormArray assignments and casts compile without the reported errors.