Update golangci-lint and tighten lint config (#190)

Bump `golangci-lint` to v2.12.2 and pin `govulncheck` to v1.3.0. Align `.golangci.yml` with the gitea repo's config: enable `revive` `var-naming` (with `skip-package-name-checks`) and drop the test-file exclusion for `errcheck`/`staticcheck`/`unparam`. Fix the now-surfaced `errcheck` violations in test handlers by discarding return values to match the existing codebase pattern.

---
This PR was written with the help of Claude Opus 4.7

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/190
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

operation/wiki/wiki_test.go

@@ -32,10 +32,10 @@ func TestWikiWriteBase64Encoding(t *testing.T) {
 			var gotBody map[string]string
 			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 				body, _ := io.ReadAll(r.Body)
-				json.Unmarshal(body, &gotBody)
+				_ = json.Unmarshal(body, &gotBody)
 				w.Header().Set("Content-Type", "application/json")
 				w.WriteHeader(http.StatusOK)
-				w.Write([]byte(`{"title":"test"}`))
+				_, _ = w.Write([]byte(`{"title":"test"}`))
 			}))
 			defer srv.Close()