Fix TestSendParallel by using only a single DB connection

see https://github.com/mattn/go-sqlite3/issues/274
see https://github.com/mattn/go-sqlite3/issues/209
see https://stackoverflow.com/questions/32479071/sqlite3-error-database-is-locked-in-golang

server/common/ginext/gin.go

@@ -13,7 +13,9 @@ func NewEngine(cfg scn.Config) *gin.Engine {
 	engine.RedirectFixedPath = false
 	engine.RedirectTrailingSlash = false
 
-	engine.Use(CorsMiddleware())
+	if cfg.Cors {
+		engine.Use(CorsMiddleware())
+	}
 
 	if cfg.GinDebug {
 		ginlogger := gin.Logger()