test: fix flaky test-webcrypto-encrypt-decrypt-aes

[Trott]

Use Object.assign() to make shallow copies of the object passed to the
test functions. The test functions are passed to Promise.all() so
execution order is not guaranteed. So using the same object in all of
them is a race condition where one test can have side effects in
another.

Fixes: #35586

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/36132/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/36135/

[targos]

Are these objects modified by the test or by core APIs?

[RaisinTen]

Are these objects modified by the test or by core APIs?

@targos Yes, the contents of plaintext is modified here:

node/test/parallel/test-webcrypto-encrypt-decrypt-aes.js

Line 20 in bcb1964

plaintext[0] = 255 - plaintext[0];

[targos]

Oh, but if we're modifying the contents of the plaintext property, a shallow copy is not going to help here.

[Trott]

Oh, but if we're modifying the contents of the plaintext property, a shallow copy is not going to help here.

🤦‍♂️ I'll run a stress test to confirm, and then make a shallow copy of the property to confirm that fixes it.

[RaisinTen]

I think something is wrong inside the function too and I think this will be a fix: #37380