It's ok to put a pass repo github.
Your pass repo is GPG encrypted using whatever private key you've selected, so it's as bullet proof as the key you've chosen. Furthermore, your private key is not stored in your pass repo. This means that the private vs. public location of your encrypted password files is not the weak link in your password manager's security. Rather, it's the private key that you've encrypted them with that you have to worry about.
Make sure it's a good key (like the one you've mentioned) and don't expose it to anyone because they won't have to crack that big ol' key to use it. They'll just have to bork your password, and, let's face it, it's really tough to be certain your password is good enough to stop everyone.
So don't let anyone else see your key. If you move your private key to each of your computers that use pass, then you can just pull your pass repo from github and use the private key stored on those computers individually. Now they'll all stay synced and safe.
Two More Things To Consider
The whole point of pass is to keep your passwords encrypted. If you're not ok with them being on github.com, then what you're really relying on is their private location and not their encrypted state. If that's the case, then why encrypt them at all? You could just use the same flat files that pass uses, and not bother encrypting them. That'd be pretty convenient!
Also, keep in mind that making your password manager easier to use means you're less likely to want/need to subvert it. Any time you have to do pass's job for it (e.g. resetting a password on an account because the nice secure one was generated on a different computer and you haven't manually synced yet, but you have to get in right now) you're gonna reduce the security it provides.