(The below is how I understand this. I am no gerrit expert, though, and I might be wrong.)
Note this part:
! [remote rejected] HEAD -> refs/publish/master/mwalker_test (change 59546 closed)
That's gerrit ("remote") telling you that the change is no good ("rejected"), because https://gerrit.wikimedia.org/r/#/c/59546/ ("change 59546") is already merged ("closed").
This means that instead of submitting the change to whatever branch you wanted to, you're actually submitting it to master.
You should either fix the .gitreview file to have something else than "defaultbranch=master" in it for your branch, or just use the good old `git push gerrit HEAD:refs/for/<branch>` command instead of `git review`.
(Or, if you did mean to submit this to master for some reason, remove the Change-Id line and have a new one generated to create a new gerrit changeset.)