GHSA-8fwc-qjw5-rvgp ClearRepoWatches fix not applied to API EditRepo path — sister code path retains stale watches on public->private

Affected: Go: code.gitea.io/gitea

## Summary

GHSA-8fwc-qjw5-rvgp ("Gitea may send release notification emails for private repositories to users whose access has been revoked", fix in PR #36319 / commit 8a98ac22) added `repo_model.ClearRepoWatches` as a defense for the state transition public→private. The cleanup was wired into `services/repository/repository.go::MakeRepoPrivate` only. The sister helper `services/repository/repository.go::updateRepository` — which is the function used by the API path `PATCH /api/v1/repos/{owner}/{repo}` — was not patched and still calls `ClearRepoStars` only.

As a result, when a public repository is flipped to private via the REST API (rather than via the web Settings → Danger Zone UI), the watch records persist. Affected users can:

- See the now-private repository in `GET /api/v1/user/subscriptions?private=true` along with its full `Repository` JSON (description, default branch, language, fork status, counts, mirror metadata, license list, etc.) — even though they have no access to the repository. - Have their stale watch records re-leak content through any future notification path that does not include the send-time `CheckRepoUnitUser` check that was added to `services/mailer/mail_release.go`. - Inflate the visible `NumWatches` counter on the repository.

## Severity

Medium — `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N`

Same impact class as the original GHSA-8fwc-qjw5-rvgp (which was classified Medium). The send-time mail filter added in the same PR mitigates the rel…