[release pipeline] OfficialBuildId value is empty in release JSON snippet

[mthalman]

In the .NET 10 Preview 4 release announcement, the JSON that gets included in the announcement content had an empty value for the OfficialBuildId field:

{
  "Channel": "10.0",
  "Runtime": "10.0.0-preview.4.25258.110",
  "Sdk": "10.0.100-preview.4.25258.110",
  "TagUrl": "https://github.com/dotnet/dotnet/releases/tag/v10.0.0-preview.4.25258.110",
  "OfficialBuildId": ""
}

This should have been set to 20250508.10. This was set correctly in the release manifest file.

[ellahathaway]

This is being completed as part of my work for dotnet/dotnet#1116

[ellahathaway]

PR: https://dev.azure.com/dnceng/internal/_git/dotnet-release/pullrequest/51571

[ellahathaway]

PR merged, closing