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