Revert "Update ClangSharp.PInvokeGenerator"

This reverts commit 7938a0c.

Author: Exanite

Directory.Packages.props

@@ -21,7 +21,7 @@
     <!-- Analyzers -->
     <PackageVersion Include="Microsoft.CodeAnalysis.Analyzers" Version="3.12.0-beta1.25218.8" />
     <!-- SilkTouch -->
-    <PackageVersion Include="ClangSharp.PInvokeGenerator" Version="21.1.8.3" />
+    <PackageVersion Include="ClangSharp.PInvokeGenerator" Version="20.1.2.4" />
     <PackageVersion Include="CSharpier.Core" Version="0.30.2" />
     <PackageVersion Include="Humanizer.Core" Version="2.14.1" />
     <PackageVersion Include="Microsoft.Build.Locator" Version="1.11.1" />