chore(deps): bump Grpc.Net.Client in /src/Flipt.Grpc (#49)

Bumps [Grpc.Net.Client](https://github.com/grpc/grpc-dotnet) from 2.55.0 to 2.67.0.
- [Release notes](https://github.com/grpc/grpc-dotnet/releases)
- [Changelog](https://github.com/grpc/grpc-dotnet/blob/master/doc/release_process.md)
- [Commits](grpc/grpc-dotnet@v2.55.0...v2.67.0)

---
updated-dependencies:
- dependency-name: Grpc.Net.Client
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

src/Flipt.Grpc/flipt-grpc.csproj

@@ -17,7 +17,7 @@
 
   <ItemGroup>
     <PackageReference Include="Google.Api.CommonProtos" Version="2.10.0" />
-    <PackageReference Include="Grpc.Net.Client" Version="2.55.0" />
+    <PackageReference Include="Grpc.Net.Client" Version="2.67.0" />
     <None Include="../../README.md" Pack="true" PackagePath="/" />
   </ItemGroup>
 </Project>