Multiple PostBuildEvent properties after conversion

[enki42]

With a lone: <PropertyGroup> <PostBuildEvent> Something here </PostBuildEvent> </PropertyGroup>

see: https://github.com/dotnet/project-system/blob/main/docs/well-known-project-properties.md

I get 4 copies in the converted project, 3 in the first property group and one in its own property group further down