tests: Use "man ls" instead of "sh"

#620 users are reporting that
"sh" has a different name used in tmux windows across platforms.

Author: tony

tests/fixtures/workspacebuilder/window_automatic_rename.yaml

@@ -6,7 +6,7 @@ windows:
     automatic-rename: on
   panes:
   - shell_command:
-    - cmd: sh
+    - cmd: man ls
     start_directory: '~'
   - shell_command:
     - cmd: echo "hey"