Fix thinko in psql test

The tests added by 14d755b000 added a
test case for psql's \set ECHO errors.  After the test, it then reset
this to \set ECHO none, which is the default.  But the regression
tests are actually run under \set ECHO all (psql -a), so that would
have been the correct way to restore the previous state.  Otherwise,
test cases added after that point would not have their input lines
displayed.  This was never the intention, so fix this now.

src/test/regress/sql/psql.sql

@@ -1315,4 +1315,4 @@ DROP TABLE oer_test;
 -- ECHO errors
 \set ECHO errors
 SELECT * FROM notexists;
-\set ECHO none
+\set ECHO all