Fix closing if block

If block using done instead of fi resulting in syntax error
on execution.

Change-Id: I31fee16fd1203c007000133b6996cf81320371f2

playbooks/python-tarball/pre.yaml

@@ -17,6 +17,6 @@
           # as we found it
           if [ -n "$TARGET_BRANCH" ]; then
               git checkout $TARGET_BRANCH || true
-          done
+          fi
         executable: /bin/bash
         chdir: "{{ zuul.projects['git.openstack.org/openstack/requirements'].src_dir }}"