Add publicGitRepoUri variable to cg-images pipeline (#7095)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lbussell

eng/pipelines/cg-images.yml

@@ -12,6 +12,8 @@ schedules:
 
 variables:
 - template: /eng/docker-tools/templates/variables/common.yml@self
+- name: publicGitRepoUri
+  value: https://github.com/dotnet/dotnet-docker
 - name: ComponentDetection.Timeout
   value: 7200 # 2 hours in seconds