Update micro benchmark properties for net8.0

Author: cincuranet

src/benchmarks/micro/MicroBenchmarks.Common.props

@@ -17,6 +17,13 @@
             <SystemVersion>7.0.0</SystemVersion>
         </PropertyGroup>
     </When>
+    <When Condition="'$(TargetFramework)' == 'net8.0'">
+        <PropertyGroup>
+            <LangVersion>12.0</LangVersion>
+            <ExtensionsVersion>8.0.*</ExtensionsVersion>
+            <SystemVersion>8.0.*</SystemVersion>
+        </PropertyGroup>
+    </When>
     <Otherwise>
         <!-- when comparing against Full .NET Framework we are usually interested in CLR differences, so net462 belongs to this block -->
         <PropertyGroup>