Fix serialization build with InheritDoc

Fixes nodatime/nodatime.serialization#117
See saucecontrol/InheritDoc#15 for rationale

build/Dockerfile

@@ -1,11 +1,6 @@
 # https://hub.docker.com/_/microsoft-dotnet
 FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
 
-# Copy .NET 6 and .NET Core 3.1 packs so that we have the XML files
-# to be used by SauceControl.InheritDoc.
-COPY --from=mcr.microsoft.com/dotnet/sdk:6.0 /usr/share/dotnet/packs /usr/share/dotnet/packs
-COPY --from=mcr.microsoft.com/dotnet/core/sdk:3.1 /usr/share/dotnet/packs /usr/share/dotnet/packs
-
 WORKDIR /source
 
 # Note: we expect to build this from a parent
@@ -14,6 +9,9 @@ COPY nodatime nodatime
 COPY nodatime.org nodatime.org
 COPY nodatime.serialization nodatime.serialization
 
+# See https://github.com/saucecontrol/InheritDoc/issues/15
+ENV NUGET_XMLDOC_MODE=none
+
 WORKDIR /source/nodatime.org/build
 RUN chmod +x *.sh
 RUN /bin/bash -c ./buildweb.sh