Normalization of GitVersionTargetFramework and fallback scenario

src/GitVersion.MsBuild/msbuild/tools/GitVersion.MsBuild.targets

@@ -8,7 +8,11 @@
         <UpdateAssemblyInfo Condition=" '$(UpdateAssemblyInfo)' == 'true' And '$(GenerateGitVersionFiles)' == 'true' ">true</UpdateAssemblyInfo>
         <GenerateGitVersionInformation Condition=" '$(GenerateGitVersionInformation)' == '' And '$(GenerateGitVersionFiles)' == 'true' ">true</GenerateGitVersionInformation>
 
-        <GitVersionTargetFramework Condition="'$(GitVersionTargetFramework)' == ''">$(TargetFramework)</GitVersionTargetFramework>
+        <!-- Validates the target framework and sets the GitVersionTargetFramework property to the target framework that is compatible with the target framework of the project -->
+        <GitVersionTargetFramework Condition="'$(GitVersionTargetFramework)' == '' and $([MSBuild]::IsTargetFrameworkCompatible($(TargetFramework), 'net8.0')) == 'true'">net8.0</GitVersionTargetFramework>
+        <GitVersionTargetFramework Condition="'$(GitVersionTargetFramework)' == '' and $([MSBuild]::IsTargetFrameworkCompatible($(TargetFramework), 'net6.0')) == 'true'">net6.0</GitVersionTargetFramework>
+        <!-- Fall back to net8.0 if the target framework is not compatible with net6.0 and net8.0 -->
+        <GitVersionTargetFramework Condition="'$(GitVersionTargetFramework)' == ''">net8.0</GitVersionTargetFramework>
         <GitVersionFileExe Condition="'$(GitVersionFileExe)' == ''">dotnet --roll-forward Major &quot;$([MSBuild]::EnsureTrailingSlash($(MSBuildThisFileDirectory)$(GitVersionTargetFramework)))gitversion.dll&quot;</GitVersionFileExe>
         <GitVersionAssemblyFile Condition="'$(GitVersionAssemblyFile)' == ''">$([MSBuild]::EnsureTrailingSlash($(MSBuildThisFileDirectory)$(GitVersionTargetFramework)))GitVersion.MsBuild.dll</GitVersionAssemblyFile>
     </PropertyGroup>