[py] Fix BrowserError issues

[bastimeyer]

Description

This fixes two issues with selenium.webdriver.common.bidi.cdp.BrowserError:

1. A KeyError can get raised when creating a new BrowserError instance when the passed obj dict/mapping doesn't have the code or message keys.
2. When the browser has sent an invalid session ID, a string incorrectly gets passed to the BrowserError constructor, which would make it raise a TypeError.

Motivation and Context

1. I noticed that issue while experimenting with Firefox's CDP v85 implementation. Apparently FF doesn't properly support devtools.fetch.enable and it returns a response with the error key (error message irrelevant):
   

   selenium/py/selenium/webdriver/common/bidi/cdp.py

   Lines 270 to 273 in 38e658a

   	if "error" in data:
   	# If the server reported an error, convert it to an exception and do
   	# not process the response any further.
   	self.inflight_result[cmd_id] = BrowserError(data["error"])

   
   That error dict however is missing the code key, hence the KeyError being raised while trying to initialize the exception.
   Since both code and message are now "optional", do you want me to add default values instead, e.g. "unknown"?
2. Simple error that could've been caught earlier if there were any typing information (which I didn't add). The error code I've added is copied from the error a few lines above. I don't know if that's correct though.
   

   selenium/py/selenium/webdriver/common/bidi/cdp.py

   Line 438 in 38e658a

   raise BrowserError({"code": -32700, "message": "Client received invalid JSON", "data": message})

No updated tests, because I couldn't find any tests which affect these parts of the code.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[CLAassistant]

All committers have signed the CLA.

[diemol]

Thank you, @bastimeyer!