[meta] fix docker image url

Author: ljharb

.github/main.workflow

@@ -1,9 +1,14 @@
-workflow "Autorebase on merge commits" {
+workflow "Autorebase PR on merge commits" {
+  on = "pull_request"
+  resolves = "rebase"
+}
+
+workflow "Autorebase branch on merge commits" {
   on = "push"
-  resolves = ["docker://ljharb/rebase:latest"]
+  resolves = "rebase"
 }
 
-action "docker://ljharb/rebase:latest" {
-  uses = "docker://ljharb/rebase:latest"
+action "rebase" {
+  uses = "ljharb/rebase:master"
   secrets = ["GITHUB_TOKEN"]
 }