Update UnbrandedGeneratorVersion to 1.0.0-alpha.20250912.1#52609

JoshLove-msft merged 1 commit intomainAzure/azure-sdk-for-net:mainfrom

typespec/update-http-client-1.0.0-alpha.20250912.1Azure/azure-sdk-for-net:typespec/update-http-client-1.0.0-alpha.20250912.1Copy head branch name to clipboard