Close the file hashes dialog box if Esc is pressed on the keyboard

[strugee]

What's the problem this feature will solve?

It's annoying to not be able to close the "Hashes" dialog box on package pages via the keyboard (at least, not without hitting Tab a million times). Example.

Definitely not a major issue, but a papercut that it would be nice to solve nonetheless :-)

Describe the solution you'd like

Hitting Esc should close this dialog box.

Additional context

I'm on Firefox 78.0.1. Thanks for maintaining PyPI, your hard work is much appreciated <3