Move temp files to results dir to avoid untracked files. (#15832)

Commit 5cae067e41e introduces test file under data dir for copy case. That will generate untracked file after regression tests. Untracked files:
```
  (use "git add <file>..." to include in what will be committed)
        src/test/regress/data/copy_no_cols.data

nothing added to commit but untracked files present (use "git add" to track)
```
Move temp date files to reuslts dir to avoid that.

Author: avamingli

src/test/regress/input/copy.source

@@ -345,8 +345,8 @@ DROP TABLE table_3_cols_dist_c3;
 CREATE TABLE table_no_cols();
 INSERT INTO table_no_cols DEFAULT VALUES;
 SELECT count(*) FROM table_no_cols;
-COPY table_no_cols TO '@abs_srcdir@/data/copy_no_cols.data' DELIMITER ',';
-COPY table_no_cols FROM '@abs_srcdir@/data/copy_no_cols.data' DELIMITER ',';
+COPY table_no_cols TO '@abs_srcdir@/results/copy_no_cols.data' DELIMITER ',';
+COPY table_no_cols FROM '@abs_srcdir@/results/copy_no_cols.data' DELIMITER ',';
 SELECT count(*) FROM table_no_cols;
 COPY table_no_cols FROM '@abs_srcdir@/data/copy.data' DELIMITER ',';
 DROP TABLE table_no_cols;

src/test/regress/output/copy.source

@@ -344,8 +344,8 @@ SELECT count(*) FROM table_no_cols;
      1
 (1 row)
 
-COPY table_no_cols TO '@abs_srcdir@/data/copy_no_cols.data' DELIMITER ',';
-COPY table_no_cols FROM '@abs_srcdir@/data/copy_no_cols.data' DELIMITER ',';
+COPY table_no_cols TO '@abs_srcdir@/results/copy_no_cols.data' DELIMITER ',';
+COPY table_no_cols FROM '@abs_srcdir@/results/copy_no_cols.data' DELIMITER ',';
 SELECT count(*) FROM table_no_cols;
  count 
 -------