Error message stylistic correction

Fixup for commit ef5e60a9d35: The inconsistent use of articles was a
bit awkward.

src/backend/parser/parse_expr.c

@@ -4772,7 +4772,7 @@ transformJsonBehavior(ParseState *pstate, JsonExpr *jsexpr,
 				targetcoll != exprcoll)
 				ereport(ERROR,
 						errcode(ERRCODE_COLLATION_MISMATCH),
-						errmsg("the collation of DEFAULT expression conflicts with RETURNING clause"),
+						errmsg("collation of DEFAULT expression conflicts with RETURNING clause"),
 						errdetail("\"%s\" versus \"%s\"",
 								  get_collation_name(exprcoll),
 								  get_collation_name(targetcoll)),

src/test/regress/expected/collate.icu.utf8.out

@@ -2711,12 +2711,12 @@ SELECT JSON_VALUE('{"a": "A"}', '$.a' RETURNING d1 DEFAULT 'C' ON EMPTY) = 'a';
 (1 row)
 
 SELECT JSON_VALUE('{"a": "A"}', '$.a' RETURNING d1 DEFAULT 'C'::d2 ON EMPTY) = 'a'; -- error
-ERROR:  the collation of DEFAULT expression conflicts with RETURNING clause
+ERROR:  collation of DEFAULT expression conflicts with RETURNING clause
 LINE 1: ...ON_VALUE('{"a": "A"}', '$.a' RETURNING d1 DEFAULT 'C'::d2 ON...
                                                              ^
 DETAIL:  "C" versus "case_insensitive"
 SELECT JSON_VALUE('{"a": "A"}', '$.a' RETURNING d1 DEFAULT 'C' COLLATE "C" ON EMPTY) = 'a'; -- error
-ERROR:  the collation of DEFAULT expression conflicts with RETURNING clause
+ERROR:  collation of DEFAULT expression conflicts with RETURNING clause
 LINE 1: ...ON_VALUE('{"a": "A"}', '$.a' RETURNING d1 DEFAULT 'C' COLLAT...
                                                              ^
 DETAIL:  "C" versus "case_insensitive"
@@ -2733,12 +2733,12 @@ SELECT JSON_VALUE('{"a": "A"}', '$.c' RETURNING d1 DEFAULT 'A' COLLATE case_inse
 (1 row)
 
 SELECT JSON_VALUE('{"a": "A"}', '$.c' RETURNING d1 DEFAULT 'A'::d2 ON EMPTY) = 'a'; -- error
-ERROR:  the collation of DEFAULT expression conflicts with RETURNING clause
+ERROR:  collation of DEFAULT expression conflicts with RETURNING clause
 LINE 1: ...ON_VALUE('{"a": "A"}', '$.c' RETURNING d1 DEFAULT 'A'::d2 ON...
                                                              ^
 DETAIL:  "C" versus "case_insensitive"
 SELECT JSON_VALUE('{"a": "A"}', '$.c' RETURNING d1 DEFAULT 'A' COLLATE "C" ON EMPTY) = 'a'; -- error
-ERROR:  the collation of DEFAULT expression conflicts with RETURNING clause
+ERROR:  collation of DEFAULT expression conflicts with RETURNING clause
 LINE 1: ...ON_VALUE('{"a": "A"}', '$.c' RETURNING d1 DEFAULT 'A' COLLAT...
                                                              ^
 DETAIL:  "C" versus "case_insensitive"