After the context has been disposed we can't route any callbacks to it
because
it is not in the map, so the assertion doesn't make sense as it always
ends up in
the top level session.
Fixes the following error:
```
pw:browser <closing ws> Closing websocket due to failed onmessage callback. eventData={"type":"success","id":32,"result":{}} e=Assertion error Error: Assertion error
pw:browser at assert (/home/yurys/playwright/packages/playwright-core/src/utils/debug.ts:21:11)
pw:browser at BidiSession.dispatchMessage (/home/yurys/playwright/packages/playwright-core/src/server/bidi/bidiConnection.ts:229:13)
pw:browser at BidiConnection.call [as _dispatchMessage] (/home/yurys/playwright/packages/playwright-core/src/server/bidi/bidiConnection.ts:93:25)
```
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