Limit type of return type of a function?

I am studying typescript with gpteachus and I got this code that i can’t wrap my head around it:

type MyFuncType = (a:number) => void

function MyFunc(a:MyFuncType) {
    return a(2)
}

MyFunc((a) => { return 'a'})

I expect typescript to prevent my from returning a string in the function! but it allows me to return a string. the expectation is to return void/empty/noting. not a string

Why typescript won’t warn me for a wrong type return?

Thanks!

I read typescript docs, I look up code examples online and via other people codebase but couldn’t find an answer