Update PowerShell benchmarks to use net8.0 (#3420)

Author: TIHan

src/benchmarks/real-world/PowerShell.Benchmarks/PowerShell.Benchmarks.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <TargetFrameworks>$(PERFLAB_TARGET_FRAMEWORKS)</TargetFrameworks>
-    <TargetFrameworks Condition="'$(TargetFrameworks)' == ''">net7.0</TargetFrameworks>
+    <TargetFrameworks Condition="'$(TargetFrameworks)' == ''">net8.0</TargetFrameworks>
     <ImplicitUsings>enable</ImplicitUsings>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <StartArguments>--filter *</StartArguments>