message: fix(docs): import SignInProviderConfig - not used
  SignInProviderConfig appears to be a superfluous import - flagged as imported but never used.
diff: @@ -165,7 +165,7 @@ Open `packages/app/src/App.tsx` and below the last `import` line, add:
  ```typescript
  import { githubAuthApiRef } from '@backstage/core-plugin-api';
  -import { SignInProviderConfig, SignInPage } from '@backstage/core-components';
  +import { SignInPage } from '@backstage/core-components';
  ```
  Search for `const app = createApp({` in this file, and below `apis,` add:
  