Add walrus operator wherever possible

[thefunkycat]

Solves #3734

I have tried to add the walrus operator wherever possible.

I went through most files.
There were a couple more instances I found where I could have added it, but it was unnecessary and would not have necessarily improved readability or code quality.

I was more lenient when it came to adding the walrus operator to tests

[thefunkycat]

@Bibo-Joshi @clot27 is there a reason the test_send_animation_url_file() and test_send_all_args() are failing? is this me? or is this a pre existing issue

[Bibo-Joshi]

Thanks for the PR! The tests are failing on some other PRs since yesterday, too. Seems like something changed in the TG servers. We'll have to investigate.

[Bibo-Joshi]

The failing tests seem to have recovered. Now only TestInlineQueryHandler.test_context_pattern is failing. I guess that's due to your changes though TBH I don't really see a flaw in those … Would you mind double check ing that?

[thefunkycat]

@Bibo-Joshi should be fixed now :)

Edit: oof the tests still fail but this is related to submitting the test coverage, all the tests pass. so not the code.

[Bibo-Joshi]

Thank you very much for the nice contribution :)