V15: Fix docker (#17722)

* Bump dotnet version

* Ensure LF line endings for shell scripts

templates/UmbracoProject/Dockerfile

@@ -1,10 +1,10 @@
-FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
+FROM mcr.microsoft.com/dotnet/aspnet:9.0 AS base
 USER $APP_UID
 WORKDIR /app
 EXPOSE 8080
 EXPOSE 8081
 
-FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
+FROM mcr.microsoft.com/dotnet/sdk:9.0 AS build
 ARG BUILD_CONFIGURATION=Release
 WORKDIR /src
 COPY ["UmbracoProject/UmbracoProject.csproj", "UmbracoProject/"]