Update dotnet version in Dockerfile

Author: olsh

Dockerfile

@@ -1,5 +1,5 @@
 # syntax=docker/dockerfile:1
-FROM mcr.microsoft.com/dotnet/aspnet:7.0
+FROM mcr.microsoft.com/dotnet/aspnet:8.0
 
 # we can't copy to a directory because WORKDIR doesn't work in buildx
 # https://github.com/docker/buildx/issues/378