This is a speculative fix to the following issue from the bots:
NON-TEST ERROR #0: UNHANDLED ERROR
TypeError: Cannot read property 'url' of undefined
at WKPage._onTargetCreated (/Users/runner/runners/2.169.1/work/playwright/playwright/src/webkit/wkPage.ts:274:12)
at process._tickCallback (internal/process/next_tick.js:68:7)
I assume that _initializeSession did swallow an error, so we erroneously
consider Page to be fully initialized (and having main frame).
