.NET 9.0.21

Release

What's Changed

• Merging internal commits for release/9.0.3xx by @dotnet-bot in #55725
• [release/9.0.3xx] Update branding to 9.0.319 by @vseanreesermsft in #56082
• Update MessagePack package version to 2.5.302 by @marcpopMSFT in #56056
• [release/9.0.3xx] Trusted roots: 2026-08 CTL by @dtivel in #56202
• [release/9.0.3xx] Update dependencies from dotnet/msbuild by @dotnet-maestro[bot] in #55959
• Merging internal commits for release/9.0.3xx by @dotnet-bot in #56209
• [release/9.0.3xx] Add new NuGet cert hash by @mmitche in #56271

Full Changelog: v9.0.318...v9.0.319