Added missing caret (^) compared to documentation

"exclude: ^(master|staging) would skip the step on master or staging,
          or any branch or tag beginning with master or staging, like master-rebase."

https://docs.cloudbees.com/docs/cloudbees-codeship/latest/pro-builds-and-configuration/steps#using-codeship-steps.yml

codeship-steps.yml

@@ -3,7 +3,7 @@
   type: push
   image_name: silintl/mysql-backup-restore
   image_tag: "{{.Branch}}"
-  exclude: (main|snyk*)
+  exclude: ^(main|snyk*)
   registry: https://index.docker.io/v1/
   encrypted_dockercfg_path: dockercfg.encrypted