test: replace localhost with os.hostname in fs-readfilesync

[lundibundi]

Fixes: #21501

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes (waiting for CI)
• tests and/or benchmarks are included
• commit message follows commit guidelines

@targos could you please try this on the setup mentioned in the issue if possible?

[nodejs-github-bot]

@lundibundi build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/1024/pipeline

[Trott]

Can you confirm that the test still works with this change if the host is disconnected from the network?

[Trott]

(Actually, if you could confirm that it works in its current form on the master branch when disconnected from the network, that would be helpful too!)

[lundibundi]

@Trott, sorry for the delay. I have run this test with/without network successfully both on master and on this branch.

Edit: I ran them on Windows 10 (10.0.17134 Build 17134), just to clarify.

[lundibundi]

CI: https://ci.nodejs.org/job/node-test-pull-request/17507/

[Trott]

This is a Windows-only test, I believe, so... @nodejs/platform-windows Can one or two folks review? @nodejs/testing too...

[addaleax]

CI: https://ci.nodejs.org/job/node-test-pull-request/17524/

[jdalton]

Neat issue and workaround.

[lundibundi]

Resume CI: https://ci.nodejs.org/job/node-test-pull-request/17540/

[danbev]

Landed in 1be804d.