Have you followed these steps?
I had missed the part where I had to add the public key via the UI page and was trying to add content to the authorized_keys directly.
I ended up using 2 keys.
1 for the gitea command to ssh from host/server to container.
1 for the client to ssh into host/server
Both keys need to be setup for the git user (or looks like gitea user for you)
I also had to ensure I had created the git user which I saw in this thread
The final thing for me since I was using 2 keys was to ensure I use ssh config file. I’m sure you would be able to do all this using a single key but when I used my approach I at least was able to get rid of the password issue.