Update UnbrandedGeneratorVersion to 1.0.0-alpha.20260218.5#56330

azure-sdk wants to merge 5 commits intomainAzure/azure-sdk-for-net:mainfrom

typespec/update-http-client-1.0.0-alpha.20260218.5Azure/azure-sdk-for-net:typespec/update-http-client-1.0.0-alpha.20260218.5Copy head branch name to clipboard