fix(jest-circus): handle undefined asyncError when test throws plain object

[JivinSardine]

Summary

When a test throws a plain object (not an Error instance) and the captured asyncError is undefined, jest-circus crashes with TypeError.

Fix

This PR adds proper null checks in two locations:

1. formatNodeAssertErrors.ts - When assigning asyncError to error, check if asyncError exists first; if not, create a new Error

2. utils.ts (_getError) - When setting asyncError.message, check if asyncError exists first; if not, return a new Error

This allows jest-circus to properly handle cases like RxJS Observables that emit plain objects as errors (common in NestJS RpcException).

Fixes #15996

[linux-foundation-easycla]

• ❌ - login: @JivinSardine / name: Jivin Sardine M . The commit (c95b433) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

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commit: c95b433