Fix locale-dependent string comparison in direct_field_access test (#2439)

Replace 'test' > 'TEST' with deterministic 'abd' > 'abc'. The original
comparison returns different results depending on system collation
settings (true under C locale, false under en_US.UTF-8).

Author: serdarmumcu

regress/expected/direct_field_access.out

@@ -78,7 +78,7 @@ $$) AS (lt agtype, gt agtype, eq agtype, ne agtype);
 (1 row)
 
 SELECT * FROM cypher('direct_access', $$
-    RETURN 'hello world' < 'hello worlds', 'test' > 'TEST'
+    RETURN 'hello world' < 'hello worlds', 'abd' > 'abc'
 $$) AS (lt agtype, gt agtype);
   lt  |  gt  
 ------+------

regress/sql/direct_field_access.sql

@@ -61,7 +61,7 @@ SELECT * FROM cypher('direct_access', $$
 $$) AS (lt agtype, gt agtype, eq agtype, ne agtype);
 
 SELECT * FROM cypher('direct_access', $$
-    RETURN 'hello world' < 'hello worlds', 'test' > 'TEST'
+    RETURN 'hello world' < 'hello worlds', 'abd' > 'abc'
 $$) AS (lt agtype, gt agtype);
 
 -- Boolean comparisons