test: add unexpected disconnect guards to http2-body-delete.js

[Kesavamoorthig06]

This relates to...

Refs: #251

Rationale

The two successful HTTP/2 DELETE tests do not check for unexpected disconnects. A silent reconnect could hide a connection error.

Changes

Use the existing guardAgainstUnexpectedDisconnect helper in both tests, as test/http2-connection.js does. The helper ignores client shutdown and idle-socket timeouts.

No production code changes.

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Review ready

Validation on Node.js v22.23.3:

• node --test test/http2-body-delete.js test/h2-disconnect-guard.js: 5 passed, 0 failed.
• npx --no-install eslint test/http2-body-delete.js: passed.
• git diff --check: passed.
• npm run test:h2:core: 120 passed, 1 failed. The failure is a Node.js onread->IsFunction() assertion in test/http2-request-never-settles.js; it also reproduces on the clean baseline with this patch removed.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.54%. Comparing base (e960331) to head (93b181f).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5970   +/-   ##
=======================================
  Coverage   91.53%   91.54%           
=======================================
  Files         113      113           
  Lines       43597    43597           
=======================================
+ Hits        39908    39911    +3     
+ Misses       3689     3686    -3     

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[Kesavamoorthig06]

The only failing jobs are Node 22 runs on test/http2-request-never-settles.js, which is unrelated to this change (+5 lines in test/http2-body-delete.js only). It's the Node 22 abort from nodejs/node#64850 (reproduces on clean baseline without this patch). Node 24/25 jobs pass.

[Kesavamoorthig06]

Synced with main, including #5961's Node 22 skip. Fresh workflows are waiting for approval. Could you approve the runs and merge if the checks pass? Thanks.