I think you’re seeing the same problem also discussed here: R-devel-el-capitan-signed.pkg fails to download when testing on R devel
Setting up the includes/excludes in the build matrix like you did sounds like the right idea to me.
I think you’re seeing the same problem also discussed here: R-devel-el-capitan-signed.pkg fails to download when testing on R devel
Setting up the includes/excludes in the build matrix like you did sounds like the right idea to me.