[build]: fixed last .NET 8.0 issue?

Directory.Build.props

@@ -73,24 +73,22 @@
     </PropertyGroup>
 
     <!--
-    For some reason, .NET 8.0 SDK release packages are referencing these but
-    older versions are present at runtime, resulting in [FileBotFoundException].
+    Projects targeting .NET 7.0 and earlier need these packages.
 
-    We're going to inject the .NET 8.0 versions of these packages into
-    all projects.
-    -->
+    WARNING: Do not reference this when targeting .NET 8.0+ unless you
+             want to debug strange "GenerateDepsFile" build problems.
 
-    <ItemGroup Condition="'$(TargetFramework)' == 'net6.0'">
-        <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="8.0.0" />
-    </ItemGroup>
+             We'll need to add another ItemGroup/condition when we
+             upgrade to .NET 9.0 and beyond in the future.
+    -->
 
-    <ItemGroup Condition="'$(TargetFramework)' == 'net7.0'">
+    <ItemGroup Condition="'$(TargetFramework)' != 'net8.0'">
         <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="8.0.0" />
     </ItemGroup>
 
-    <ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">
-        <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="8.0.0" />
-    </ItemGroup>
+    <Target Name="CheckBclPackageRefs" BeforeTargets="Compile" Condition="'$(TargetFramework)' == 'net9.0'">
+        <Error Text="Add a new [Microsoft.Bcl.AsyncInterfaces] package reference exclusion for .net9.0 and update this target condition to net10.0." />
+    </Target>
 
     <!-- 
     We have a somewhat complex build environment.  The NEONCLOUD repo is private and