chore(deps): update crazy-max/ghaction-import-gpg action to v6 (#736)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [crazy-max/ghaction-import-gpg](https://github.com/crazy-max/ghaction-import-gpg) | action | major | `v5` -> `v6` |

---

### Release Notes

<details>
<summary>crazy-max/ghaction-import-gpg (crazy-max/ghaction-import-gpg)</summary>

### [`v6`](https://github.com/crazy-max/ghaction-import-gpg/compare/v5...v6)

[Compare Source](https://github.com/crazy-max/ghaction-import-gpg/compare/v5...v6)

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzOS4yMDcuMyIsInVwZGF0ZWRJblZlciI6IjM5LjIwNy4zIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6W119-->

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-on: https://gitea.com/gitea/tea/pulls/736
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Renovate Bot <renovate-bot@gitea.com>
Co-committed-by: Renovate Bot <renovate-bot@gitea.com>

.gitea/workflows/release-nightly.yml

@@ -17,7 +17,7 @@ jobs:
           go-version-file: "go.mod"
       - name: import gpg
         id: import_gpg
-        uses: crazy-max/ghaction-import-gpg@v5
+        uses: crazy-max/ghaction-import-gpg@v6
         with:
           gpg_private_key: ${{ secrets.GPGSIGN_KEY }}
           passphrase: ${{ secrets.GPGSIGN_PASSPHRASE }}