Since 898e5e32, this command uses partially ShareUpdateExclusiveLock,
but the docs did not get the call.

Author: Justin Pryzby
Reviewed-by: Amit Langote, Álvaro Herrera, Michael Paquier
Discussion: https://postgr.es/m/20191028001207.GB23808@telsasoft.com
Backpatch-through: 12