Bump Google.Api.CommonProtos from 2.13.0 to 2.15.0 in /dotnet-etcd

Bumps [Google.Api.CommonProtos](https://github.com/googleapis/gax-dotnet) from 2.13.0 to 2.15.0.
- [Release notes](https://github.com/googleapis/gax-dotnet/releases)
- [Changelog](https://github.com/googleapis/gax-dotnet/blob/main/CHANGELOG.md)
- [Commits](googleapis/gax-dotnet@Google.Api.CommonProtos-2.13.0...Google.Api.CommonProtos-2.15.0)

---
updated-dependencies:
- dependency-name: Google.Api.CommonProtos
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

dotnet-etcd/dotnet-etcd.csproj

@@ -57,7 +57,7 @@ Advanced uses take advantage of the consistency guarantees to implement database
 
 
   <ItemGroup>
-    <PackageReference Include="Google.Api.CommonProtos" Version="2.13.0" />
+    <PackageReference Include="Google.Api.CommonProtos" Version="2.15.0" />
     <PackageReference Include="Google.Protobuf" Version="3.25.1" />
     <PackageReference Include="Grpc.Net.Client" Version="2.60.0" />
     <PackageReference Include="Grpc.Tools" Version="2.60.0">