docs: fix incorrect plpgsql error message
Change "$1" to "username".
Reported-by: philipp(dot)salvisberg(at)gmail(dot)com
Discussion: https://postgr.es/m/172112109590.736590.12219129462878821880@wrigleys.postgresql.org
Backpatch-through: 12
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/03e9b958eef44046c0092f1f34da4b2de0f9071d
Modified Files
--------------
doc/src/sgml/plpgsql.sgml | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)