You’ve got an existing srcdir, a file has changed, and the new one won’t merge, probably because you didn’t clean build? Try a clean build instead.
If you read the output from your post above, you can see where yay is asking you if you want to cleanbuild your packages. Instead of just hitting enter, select a or 1 at that prompt.
In general, whenever you have an issue building a package you should first try a clean build.
You may need to import manually if you’re using a broken keyserver, or just switch your default to a working keyserver hkps://keyserver.ubuntu.com in $HOME/.gnupg/gpg.conf for AUR package keys and /etc/pacman.d/gnupg/gpg.conf for repo package keys.