Updated Build.cs to version from master

nukebuild/Build.cs

@@ -122,6 +122,14 @@ partial class Build : NukeBuild
         
         foreach(var fw in frameworks)
         {
+            if (fw.StartsWith("net4")
+                && RuntimeInformation.IsOSPlatform(OSPlatform.Linux) 
+                && Environment.GetEnvironmentVariable("FORCE_LINUX_TESTS") != "1")
+            {
+                Information($"Skipping {fw} tests on Linux - https://github.com/mono/mono/issues/13969");
+                continue;
+            }
+
             Information("Running for " + fw);
             DotNetTest(c =>
             {