MINOR: [C#] Bump Microsoft.Bcl.AsyncInterfaces in /csharp

Bumps [Microsoft.Bcl.AsyncInterfaces](https://github.com/dotnet/runtime) from 6.0.0 to 7.0.0.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v6.0.0...v7.0.0)

---
updated-dependencies:
- dependency-name: Microsoft.Bcl.AsyncInterfaces
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

csharp/src/Apache.Arrow.Flight/Apache.Arrow.Flight.csproj

@@ -11,7 +11,7 @@
  </ItemGroup>
 
  <ItemGroup Condition="'$(TargetFramework)'=='netstandard2.0'">
- <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="6.0.0" />
+ <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="7.0.0" />
  </ItemGroup>
 
  <ItemGroup>