pushManager is missing from ServiceWorkerRegistration

[jakebailey]

This happened in #2190

Leading to:

Error in serviceworker-webpack-plugin
Error: 
/home/runner/work/DefinitelyTyped/DefinitelyTyped/types/serviceworker-webpack-plugin/serviceworker-webpack-plugin-tests.ts
  49:22  error  TypeScript@6.0 compile error: 
Property 'pushManager' does not exist on type 'ServiceWorkerRegistration'  @definitelytyped/expect
  53:22  error  TypeScript@6.0 compile error: 
Property 'pushManager' does not exist on type 'ServiceWorkerRegistration'  @definitelytyped/expect

✖ 2 problems (2 errors, 0 warnings)

But, it seems like it should be there: https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerRegistration/pushManager

[jakebailey]

I have a fix, though with github being broken I couldn't send it. Perhaps your fix will be better (just saw the self-assign)