Add warning about JetBrains.Annotations

JetBrains/JetBrains.Annotations#45

Author: ltrzesniewski

src/Directory.Build.props

@@ -38,7 +38,8 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="JetBrains.Annotations" Version="2024.3.0" PrivateAssets="all" />
+    <!-- Do not update beyond 2024.3.0, later versions do not use [Conditional] anymore -->
+    <PackageReference Include="JetBrains.Annotations" Version="[2024.3.0]" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>