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 86.92%. Comparing base (9ec5a2e) to head (592fac9).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5970      +/-   ##
==========================================
- Coverage   86.92%   86.92%   -0.01%     
==========================================
  Files         115      115              
  Lines       45749    45749              
==========================================
- Hits        39767    39766       -1     
- Misses       5982     5983       +1     

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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.