issue #587: attempt to fix Mac Azure job

.ci/prep_azure.py

@@ -7,7 +7,8 @@ import ci_lib
 
 batches = []
 
-batches += [
+if os.uname()[0] == 'Linux':
+    batches += [
         [
             "sudo chown `whoami`: ~",
             "chmod u=rwx,g=rx,o= ~",
@@ -27,7 +28,7 @@ batches += [
             "cat tests/data/docker/mitogen__has_sudo_pubkey.key.pub > ~/.ssh/authorized_keys",
             "chmod u=rw,go=r ~/.ssh/authorized_keys",
         ]
-]
+    ]
 
 if ci_lib.have_apt():
     batches.append([