C#: Upgrade Roslyn dependencies to 3.9

Author: tamasvajk

csharp/extractor/Semmle.Extraction.CSharp/Semmle.Extraction.CSharp.csproj

@@ -20,7 +20,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.8.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.9.0" />
   </ItemGroup>
 
 </Project>

csharp/extractor/Semmle.Extraction/Semmle.Extraction.csproj

@@ -15,7 +15,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis" Version="3.8.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis" Version="3.9.0" />
     <PackageReference Include="GitInfo" Version="2.0.20">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>