Re-stabilize infinite_recurse() test case.

Since commit 8f59f6b9c0, CLOBBER_CACHE_ALWAYS buildfarm members have
been failing this test case because the error message now sometimes
includes an error cursor position.  It seems largely just luck that
that never happened before, and there are likely to be more ways it
could happen in future.  Hence, rather than trying to prevent it,
adjust the test script to suppress that component of the report.

At some point we might need to back-patch this, but refrain until
there's a demonstrated need.  (We'd need a different fix before v12,
anyway, since VERBOSITY=sqlstate is a recent thing.)

Tom Lane and Andres Freund

Discussion: https://postgr.es/m/30675.1586111599@sss.pgh.pa.us

src/test/regress/sql/errors.sql

@@ -366,8 +366,10 @@ NOT
 NULL);
 
 -- Check that stack depth detection mechanism works and
--- max_stack_depth is not set too high
+-- max_stack_depth is not set too high.  The full error report is not
+-- very stable, so show only SQLSTATE and primary error message.
 create function infinite_recurse() returns int as
 'select infinite_recurse()' language sql;
-\set VERBOSITY terse
+\set VERBOSITY sqlstate
 select infinite_recurse();
+\echo :LAST_ERROR_MESSAGE