Fix key signature error page (#22229) (#22231)

Fix key signature error page (#22229) (#22231)

- Backport of #22229
- When the GPG key contains an error, such as an invalid signature or an
email address that does not match the user.A page will be shown that
says you must provide a signature for the token.
- This page had two errors: one had the wrong translation key and the
other tried to use an undefined variable
[`.PaddedKeyID`](https://github.com/go-gitea/gitea/blob/e81ccc406bf723a5a58d685e7782f281736affd4/models/asymkey/gpg_key.go#L65-L72),
which is a function implemented on the `GPGKey` struct, given that we
don't have that, we use
[`KeyID`](https://github.com/go-gitea/gitea/blob/e81ccc406bf723a5a58d685e7782f281736affd4/routers/web/user/setting/keys.go#L102)
which is [the fingerprint of the
publickey](https://pkg.go.dev/golang.org/x/crypto/openpgp/packet#PublicKey.KeyIdString)
and is a valid way for opengpg to refer to a key.

<!--

Please check the following:

1. Make sure you are targeting the `main` branch, pull requests on
release branches are only allowed for bug fixes.
2. Read contributing guidelines:
https://github.com/go-gitea/gitea/blob/main/CONTRIBUTING.md
3. Describe what your pull request does and which issue you're targeting
(if any)

-->