Fall back to net10.0 when SDK folder has no version

Visual Studio MSBuild SDK path has no version, so Version.Parse failed.

Author: rokups

eng/SharpCpp.Build.props

@@ -37,7 +37,9 @@
     <SharpCppE2ENativeLibraryPath>$(SharpCppOutputDir)/$(SharpCppSharedLibraryPrefix)SharpCppTestsE2E_Native$(SharpCppSharedLibrarySuffix)</SharpCppE2ENativeLibraryPath>
 
     <SharpCppSdkVersion>$([System.IO.Path]::GetFileName($([System.IO.Path]::GetDirectoryName('$(MSBuildSDKsPath)'))))</SharpCppSdkVersion>
-    <TargetFramework Condition="'$(TargetFramework)' == ''">net$([System.Version]::Parse('$(SharpCppSdkVersion)').Major).0</TargetFramework>
+    <TargetFramework Condition="'$(TargetFramework)' == '' and $([System.Text.RegularExpressions.Regex]::IsMatch('$(SharpCppSdkVersion)', '^[0-9]+\.[0-9]+'))">net$([System.Version]::Parse('$(SharpCppSdkVersion)').Major).0</TargetFramework>
+    <!-- Visual Studio MSBuild keeps its SDKs in a folder that has no version in its name. -->
+    <TargetFramework Condition="'$(TargetFramework)' == ''">net10.0</TargetFramework>
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <LangVersion>latest</LangVersion>