chore(deps): update workflow action versions (#792)

## Summary
- `actions/checkout`: v4/v5 → v6
- `actions/setup-go`: v5 → v6
- `docker/build-push-action`: v5 → v6

All other actions (`goreleaser/goreleaser-action@v6`, `docker/setup-qemu-action@v3`, `docker/setup-buildx-action@v3`, `docker/login-action@v3`, `crazy-max/ghaction-import-gpg@v6`) were already at their latest major versions.

No breaking changes affect the current workflow configurations. The main changes in the updated actions are Node.js 24 runtime upgrades and minor feature additions.

Reviewed-on: https://gitea.com/gitea/act_runner/pulls/792
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

.gitea/workflows/test.yml

@@ -8,8 +8,8 @@ jobs:
     name: check and test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-go@v5
+      - uses: actions/checkout@v6
+      - uses: actions/setup-go@v6
         with:
           go-version-file: 'go.mod'
       - name: vet checks