test: improve error output of test-http2-client-promisify-connect-error

[aduh95]

I'm getting a quite useless error output on Nix CI, showing there's a failed assertion but not showing the actual assertion error. Using assert.rejects should improve it greatly, and also makes the test code more readable.

For reference, the current output is:

not ok 1611 parallel/test-http2-client-promisify-connect-error --- duration_ms: 70.93100 severity: fail exitcode: 1 stack: |- node:internal/process/promises:394 triggerUncaughtException(err, true /* fromPromise */); ^ AssertionError [ERR_ASSERTION]: Expected values to be strictly equal: + actual - expected + 'ERR_ASSERTION' - 'ECONNREFUSED' at /build/node-v22.14.0/test/parallel/test-http2-client-promisify-connect-error.js:21:16 at /build/node-v22.14.0/test/common/index.js:435:15 at process.processTicksAndRejections (node:internal/process/task_queues:105:5){generatedMessage: true, code: 'ERR_ASSERTION', actual: 'ERR_ASSERTION', expected: 'ECONNREFUSED', operator: 'strictEqual' } Node.js v22.14.0 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.03%. Comparing base (baa60ce) to head (6a8c8ae).
Report is 15 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #57135 +/- ## ========================================== - Coverage 89.03% 89.03% -0.01%  ========================================== Files 665 665 Lines 193408 193408 Branches 37279 37281 +2 ========================================== - Hits 172206 172205 -1 + Misses 13886 13881 -5 - Partials 7316 7322 +6 

see 28 files with indirect coverage changes

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/65317/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/65322/

[nodejs-github-bot]

Landed in 8fc919d