Renovate should not update to versions from non-release branches

Author: AArnott

.github/renovate.json

@@ -16,6 +16,11 @@
 			"matchDatasources": ["dotnet-version", "docker"],
 			"matchDepNames": ["dotnet-sdk", "mcr.microsoft.com/dotnet/sdk"],
 			"groupName": "Dockerfile and global.json updates"
+		},
+		{
+			"matchPackageNames": ["*"],
+			"allowedVersions": "!/-g[a-f0-9]+$/",
+			"groupName": "Ignore versions built from non-release branches"
 		}
 	]
 }