Fix linting.

.golangci.yml

@@ -17,6 +17,7 @@ linters:
     - varnamelen
     - noinlineerr
     - wsl
+    - gomodguard # deprecated
   settings:
     cyclop:
       max-complexity: 30

go.mod

@@ -1,3 +1,3 @@
 module go.dev.pztrn.name/vikunja-notifier
 
-go 1.26.4
+go 1.26.3

internal/services/core/httpserver/server.go

@@ -50,6 +50,7 @@ func (h *httpServer) configureHTTPServer() error {
 
 func (h *httpServer) RegisterHandler(method, path string, handler http.HandlerFunc) {
 	h.httpMux.HandleFunc(fmt.Sprintf("%s %s", method, path), func(w http.ResponseWriter, r *http.Request) {
+		//nolint:modernize
 		for i := len(h.middlewares) - 1; i >= 0; i-- {
 			handler = h.middlewares[i](handler)
 		}