Update traefik version used in HTTPS config (#6164)

Just to match version used in docker-compose.yml

I just think Someone forgot about updating it when version from
docker-compose.yml was updated (
https://github.com/opencv/cvat/commit/980c019427422e4a13e9f5b3c7c20de3264513cb
)

docker-compose.https.yml

@@ -14,7 +14,7 @@ services:
       - traefik.http.routers.cvat-ui.tls.certresolver=lets-encrypt
 
   traefik:
-    image: traefik:v2.4
+    image: traefik:v2.9
     container_name: traefik
     command:
       - "--providers.docker.exposedByDefault=false"