Bump Godot.NET.Sdk and SourceGenerators versions

Bump `Godot.NET.Sdk` to version 4.0.0-dev6.
Bump `Godot.SourceGenerators` to version 4.0.0-dev3.
Use floating version 4.0.*-* for package references in Sdk.

modules/mono/SdkPackageVersions.props

@@ -1,6 +1,7 @@
 <Project>
   <PropertyGroup>
-    <PackageVersion_Godot_NET_Sdk>4.0.0-dev5</PackageVersion_Godot_NET_Sdk>
-    <PackageVersion_Godot_SourceGenerators>4.0.0-dev2</PackageVersion_Godot_SourceGenerators>
+    <PackageFloatingVersion_Godot>4.0.*-*</PackageFloatingVersion_Godot>
+    <PackageVersion_Godot_NET_Sdk>4.0.0-dev6</PackageVersion_Godot_NET_Sdk>
+    <PackageVersion_Godot_SourceGenerators>4.0.0-dev3</PackageVersion_Godot_SourceGenerators>
   </PropertyGroup>
 </Project>

modules/mono/editor/Godot.NET.Sdk/Godot.NET.Sdk/Sdk/Sdk.targets

@@ -17,6 +17,6 @@
 
   <!-- C# source generators -->
   <ItemGroup Condition=" '$(DisableImplicitGodotGeneratorReferences)' != 'true' ">
-    <PackageReference Include="Godot.SourceGenerators" Version="$(PackageVersion_Godot_SourceGenerators)" />
+    <PackageReference Include="Godot.SourceGenerators" Version="$(PackageFloatingVersion_Godot)" />
   </ItemGroup>
 </Project>