Bump Microsoft.EntityFrameworkCore (#43499)

Bumps the dotnet group in /docs/csharp/language-reference/compiler-messages/snippets/null-warnings with 1 update: [Microsoft.EntityFrameworkCore](https://github.com/dotnet/efcore).


Updates `Microsoft.EntityFrameworkCore` from 8.0.10 to 9.0.0
- [Release notes](https://github.com/dotnet/efcore/releases)
- [Commits](dotnet/efcore@v8.0.10...v9.0.0)

---
updated-dependencies:
- dependency-name: Microsoft.EntityFrameworkCore
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: dotnet
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/csharp/language-reference/compiler-messages/snippets/null-warnings/null-warnings.csproj

@@ -9,7 +9,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="8.0.10" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="9.0.0" />
   </ItemGroup>
 
 </Project>