BUG #16683: explain plan format xml produces invalid xml

The following bug has been logged on the website:

Bug reference:      16683
Logged by:          Frits Jalvingh
Email address:      jal@etc.to
PostgreSQL version: 13.0
Operating system:   Ubuntu 20.04
Description:

I am running an explain plan:
explain (format xml,analyze,costs,verbose,timing,buffers) .....
The result contains the following part which is invalid XML:

                    <Incremental-Sort-Groups>
                        <Group-Count>4</Group-Count>
                        <Sort-Methods-Used>
                            <Item>quicksort</Item>
                        </Sort-Methods-Used>
                        <Sort-Space>
                            <Average-Sort-Space-Used>30</Average-Sort-Space-Used>
                            <Peak-Sort-Space-Used>30</Peak-Sort-Space-Used>
                        </Sort-Spaces>
                    </Incremental-Sort-Groups>
Sort-Space is incorrectly finished with /Sort-Spaces