fix(ci): revert PUBLIC_ECR_NAMESPACE back to z5c7y9u9

r1l9t0r6 belongs to account 888577024788; the PUBLIC_AWS_ROLE_TO_ASSUME
(github-actions-ecr-push) lives in account 496607027995 whose public ECR
alias is z5c7y9u9 -- same as strata-bridge.

Author: Madan Shah

.github/workflows/docker-publish-ecr.yml

@@ -20,7 +20,7 @@ env:
   ECR_REGISTRY: ${{ vars.ECR_REGISTRY || '888577024788.dkr.ecr.us-east-1.amazonaws.com' }}
   ECR_REPOSITORY: ${{ vars.ECR_REPOSITORY || 'tn1/mosaic' }}
   PUBLIC_ECR_REGISTRY: public.ecr.aws
-  PUBLIC_ECR_NAMESPACE: r1l9t0r6
+  PUBLIC_ECR_NAMESPACE: z5c7y9u9
   PUBLIC_ECR_REPOSITORY: mosaic
   PUBLIC_ECR_REGION: us-east-1
   DEFAULT_BUILD_REF: bae62a54b7137e811653d5dd89975e10f0e71676