I do see a point in it working like it does, though. I'm one of the lead developers on a free software project with over 20 years of history. Even though the project has used multiple version control systems (and hosting providers) over time, we have imported our entire project's history going back to the very first commit into git and GitHub. Not every contributor has kept their email address for over 20 years. Some…
Well, tough luck? I don't think it's that important. Just accept it as a fact of life: you lost access to your email account and can't verify you still own it (you don't, clearly).
GitHub should just show the e-mail address when it can't associate that to an account, maybe show it's unverified and link to a help page explaining anyone could have faked that in the commit. I don't understand why they care so much to put a face (the GH account) on the commit when the address is not verified.