Update Image Builder tag reference

Author: dotnet-docker-bot

Diff for: eng/common/templates/variables/docker-images.yml

@@ -1,5 +1,5 @@
 variables:
-  imageNames.imageBuilderName: mcr.microsoft.com/dotnet-buildtools/image-builder:2662183
+  imageNames.imageBuilderName: mcr.microsoft.com/dotnet-buildtools/image-builder:2684339
   imageNames.imageBuilder: $(imageNames.imageBuilderName)
   imageNames.imageBuilder.withrepo: imagebuilder-withrepo:$(Build.BuildId)-$(System.JobId)
   imageNames.testRunner: mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux3.0-docker-testrunner