Release .NET 9.0.12 · dotnet/aspnetcore

What's Changed

Update branding to 9.0.12 by @vseanreesermsft in #64248
Update Microsoft.Build versions to 17.8.43 by @MackinnonBuck in #64277
[release/9.0] (deps): Bump src/submodules/googletest from 9706f75 to 6ec14df by @dependabot[bot] in #64230
[release/9.0] Update dependencies from dotnet/extensions by @dotnet-maestro[bot] in #64111
[release/9.0] Update dependencies from dotnet/arcade by @dotnet-maestro[bot] in #64065
[release/9.0] Upgrade to MacOS 15 for CI by @wtgodbe in #64310
Merging internal commits for release/9.0 by @vseanreesermsft in #64312
[release/9.0] Don't use netcoreapp2.1 in dotnet-get-document by @wtgodbe in #64351
[release/9.0] AppContext for HttpSys CBT hardening by @BrennanConroy in #64297
[release/9.0] Update dependencies from dotnet/arcade by @dotnet-maestro[bot] in #64350
[release/9.0] Update dependencies from dotnet/extensions by @dotnet-maestro[bot] in #64388
[release/9.0] Delete signalr-daily-tests.yml by @github-actions[bot] in #64589
[release/9.0] (deps): Bump src/submodules/googletest from 6ec14df to 1b96fa1 by @dependabot[bot] in #64580
[release/9.0] Update dependencies from dotnet/extensions by @dotnet-maestro[bot] in #64503

Full Changelog: v9.0.11...v9.0.12