Update version to .NET 8.0

Author: pgrawehr

src/devices/Directory.Build.props

@@ -3,9 +3,9 @@
 
   <PropertyGroup>
     <!-- Most projects should use this value to build for all possible target frameworks -->
-    <DefaultBindingTfms>net6.0;</DefaultBindingTfms>
-    <DefaultSampleTfms>net6.0</DefaultSampleTfms>
-    <DefaultTestTfms>net6.0</DefaultTestTfms>
+    <DefaultBindingTfms>net8.0</DefaultBindingTfms>
+    <DefaultSampleTfms>net8.0</DefaultSampleTfms>
+    <DefaultTestTfms>net8.0</DefaultTestTfms>
     <NoWarn>$(NoWarn);CS8321</NoWarn>
     <DeterministicSourcePaths>false</DeterministicSourcePaths>
     <IsPackable>false</IsPackable>