[v15.0/forgejo] Exclude SSH certificate principals from output when viewing user's SSH keys (#12166)

**Backport:** https://codeberg.org/forgejo/forgejo/pulls/12079

Fixes #11590

When viewing a user's SSH keys, SSH principals are now excluded from the output.  This would previously either result in a panic in [OmitEmail](cfd4d53e32/models/asymkey/ssh_key.go (L67)), if the principal name didn't contain any spaces, or truncate the principal name, if it did contain spaces.

The TestExportUserSSHKeys test was also updated and fails if the fix(commit cfcbc33af0) is reverted.

## Checklist

The [contributor guide](https://forgejo.org/docs/next/contributor/) contains information that will be helpful to first time contributors. All work and communication must conform to Forgejo's [AI Agreement](https://codeberg.org/forgejo/governance/src/branch/main/AIAgreement.md). There also are a few [conditions for merging Pull Requests in Forgejo repositories](https://codeberg.org/forgejo/governance/src/branch/main/PullRequestsAgreement.md). You are also welcome to join the [Forgejo development chatroom](https://matrix.to/#/#forgejo-development:matrix.org).

### Tests for Go changes

- I added test coverage for Go changes...
  - [ ] in their respective `*_test.go` for unit tests.
  - [x] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I ran...
  - [x] `make pr-go` before pushing
  - [x] `make test`
  - [x] `make test-sqlite#TestExportUserSSHKeys`

I have also manually tested the change.

The full integration tests(`make test-sqlite`) report some errors, but I get the same errors without this PR(tested on commit [6a5dda7116](6a5dda7116)).

I have not tested with the other database backends.

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [x] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [ ] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.

*The decision if the pull request will be shown in the release notes is up to the mergers / release team.*

The content of the `release-notes/<pull request number>.md` file will serve as the basis for the release notes. If the file does not exist, the title of the pull request will be used instead.

<!--start release-notes-assistant-->

## Release notes
<!--URL:https://codeberg.org/forgejo/forgejo-->
- Bug fixes
  - [PR](https://codeberg.org/forgejo/forgejo/pulls/12166): <!--number 12166 --><!--line 0 --><!--description RXhjbHVkZSBTU0ggY2VydGlmaWNhdGUgcHJpbmNpcGFscyBmcm9tIG91dHB1dCB3aGVuIHZpZXdpbmcgdXNlcidzIFNTSCBrZXlz-->Exclude SSH certificate principals from output when viewing user's SSH keys<!--description-->
<!--end release-notes-assistant-->

Co-authored-by: Alec Walsh <code@alecwalsh.name>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/12166
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Co-authored-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
Co-committed-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>

routers/web/user/home.go

@@ -705,6 +705,9 @@ func ShowSSHKeys(ctx *context.Context) {
 
 	var buf bytes.Buffer
 	for i := range keys {
+		if keys[i].Type == asymkey_model.KeyTypePrincipal {
+			continue // Don't display SSH principals, only public keys
+		}
 		buf.WriteString(keys[i].OmitEmail())
 		buf.WriteString("\n")
 	}