Remove TestWindowsNet60 build target (#619)

* Remove `TestWindowsNet60` build target

* Update Nuke build schema

Author: rhysparry

.nuke/build.schema.json

@@ -96,7 +96,6 @@
               "TestLinux",
               "TestWindows",
               "TestWindowsNet48",
-              "TestWindowsNet60",
               "TestWindowsNet80"
             ]
           }
@@ -123,7 +122,6 @@
               "TestLinux",
               "TestWindows",
               "TestWindowsNet48",
-              "TestWindowsNet60",
               "TestWindowsNet80"
             ]
           }

build/Build.cs

@@ -111,11 +111,6 @@ ITargetDefinition CompileDefinition(ITargetDefinition targetDefinition, [CanBeNu
     [PublicAPI]
     Target TestWindowsNet80 => _ => TestDefinition(_, CompileNet80, "net8.0", runDotMemoryTests: false);
 
-    // This temporary target is included to run the net8 tests on a pipeline configured for net6.0
-    // It can be removed once the build pipeline is updated to reference the new target.
-    [PublicAPI]
-    Target TestWindowsNet60 => t => t.DependsOn(TestWindowsNet80);
-
     ITargetDefinition TestDefinition(ITargetDefinition targetDefinition, Target dependsOn, [CanBeNull] string framework, bool runDotMemoryTests)
     {
         return targetDefinition