ci(cd): drop hardcoded master- sha tag

The ref_name-prefixed sha tag (`type=sha,prefix=${{ github.ref_name }}-`)
already produces `master-<sha>` on master builds and the correct prefix
on dispatch from other branches, so the hardcoded master- variant was
redundant and incorrect off-master.

Author: quangdangfit

.github/workflows/cd.yml

@@ -129,7 +129,6 @@ jobs:
             type=ref,event=branch
             type=ref,event=tag
             type=sha,format=short,prefix=${{ github.ref_name }}-
-            type=sha,prefix=master-,format=short
 
       - name: Create manifest list and push
         working-directory: /tmp/digests