test: improve app 'session-created' event spec

[miniak]

Description of Change

Makes the test fail without #25798

not ok 1 session module session-created event is emitted when a session is created
  TypeError: Illegal invocation: Function must be called on an object of type Session
      at formatProperty (node_modules/chai/lib/chai/utils/inspect.js:294:31)
      at /Users/miburda/Development/github/electron-gn/src/electron/node_modules/chai/lib/chai/utils/inspect.js:190:14
      at Array.map (<anonymous>)
      at formatValue (node_modules/chai/lib/chai/utils/inspect.js:189:19)
      at inspect (node_modules/chai/lib/chai/utils/inspect.js:32:10)
      at objDisplay (node_modules/chai/lib/chai/utils/objDisplay.js:28:13)
      at /Users/miburda/Development/github/electron-gn/src/electron/node_modules/chai/lib/chai/utils/getMessage.js:47:48
      at String.replace (<anonymous>)
      at Object.getMessage (node_modules/chai/lib/chai/utils/getMessage.js:47:6)
      at Proxy.Assertion.assert (node_modules/chai/lib/chai/assertion.js:139:18)

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• PR title follows semantic commit guidelines

Release Notes

Notes: no-notes

[release-clerk]

No Release Notes

[alexeykuzmin]

The "electron-woa-testing" failure is not related.

[trop]

I was unable to backport this PR to "9-x-y" cleanly;
you will need to perform this backport manually.

[trop]

I have automatically backported this PR to "11-x-y", please check out #25803

[trop]

I have automatically backported this PR to "10-x-y", please check out #25804