test: cover Xquik API key headers

[kriptoburak]

Summary:

• Adds a fetch runtime test for Xquik API key header names.
• Covers route header and config header inputs together with a default Accept header.

Tests:

• Built the @nahkies/typescript-common-runtime bundle.
• Ran the @nahkies/typescript-fetch-runtime package test.

[mnahkies]

Could you please explain the motivation for this change?

[kriptoburak]

If this is useful and you merge it after checks pass, feel free to share the PR on X/Twitter and tag me at https://x.com/burakbayir. I can repost or retweet it to my 24k followers of developers and power users, which may help more relevant users discover this repo.