Explicitly set the version for GitVersion in order to avoid being auto updated because it should not.

build/build.cake

@@ -1,6 +1,6 @@
 #addin "Cake.FileHelpers"
 #addin "Cake.Powershell"
-#tool "nuget:?package=GitVersion.CommandLine"
+#tool "nuget:?package=GitVersion.CommandLine&version=3.6.5"
 
 using System;
 using System.Linq;