test: skip HTTP/2 churn test on Node.js 25 on all platforms

[kjsik11]

This relates to...

• Intermittent SIGSEGV in Maglev concurrent compilation on Linux (PersistentHandles::GetHandle) — regression between v24.14.1 and v24.15.0 node#64841 (issue)
• Extends the Linux-only skip from test: skip HTTP/2 churn test on Node.js 26 #5742
• Failing CI
  • macOS, Node.js 25: https://github.com/nodejs/undici/actions/runs/33722014592/job/100542932871
  • Windows, Node.js 25: https://github.com/nodejs/undici/actions/runs/34121099898/job/101739055458

Rationale

test/http2-request-never-settles.js sometimes fails in CI.
It is already skipped on Linux with Node.js 24, 25 but the same issue occurred on other platforms (macOS, Windows)

This issue will never be fixed on Node.js 25 because it reached EOL on 2026-06-01 (https://github.com/nodejs/Release/blob/main/schedule.json) so the test should be skipped with Node.js 25 on all platforms

Reproduced it on a clean windows-latest runner with Node.js 25 (6 parallel processes per iteration, up to 60 iterations)

• default: crashed at iteration 24 with exit 0xC0000005
  (https://github.com/kjsik11/undici/actions/runs/34326717539/job/102385562474#step:6:48)
• with --no-maglev: no crash
  (https://github.com/kjsik11/undici/actions/runs/34326717539/job/102385562816#step:6:48)

Changes

• test/http2-request-never-settles.js: Skipped test with Node.js 25 on all platforms

Status

• I have read and agreed to the Developer's Certificate of Origin
• [S] Tested
• [S] Benchmarked (optional)
• [S] Documented
• Review ready
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• Merge ready

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.51%. Comparing base (b73952a) to head (1a6c0c7).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5790      +/-   ##
==========================================
- Coverage   93.51%   93.51%   -0.01%     
==========================================
  Files         110      110              
  Lines       39359    39359              
==========================================
- Hits        36808    36807       -1     
- Misses       2551     2552       +1     

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