Back off output precision in circle.sql regression test.

We were setting extra_float_digits = 0 to avoid platform-dependent
output in this test, but that's still able to expose platform-specific
roundoff behavior in some new test cases added by commit a3d284485,
as reported by Peter Eisentraut.  Reduce it to -1 to hide that.

(Over in geometry.sql, we're using -3, which is an ancient decision
dating to 337f73b1b.  I wonder whether that's overkill now.  But
there's probably little value in trying to change it.)

Back-patch to v12 where a3d284485 came in; there's no evidence that
we have any platform-dependent issues here before that.

Discussion: https://postgr.es/m/15551268-e224-aa46-084a-124b64095ee3@2ndquadrant.com

src/test/regress/expected/circle.out

@@ -1,8 +1,9 @@
 --
 -- CIRCLE
 --
--- avoid bit-exact output here because operations may not be bit-exact.
-SET extra_float_digits = 0;
+-- Back off displayed precision a little bit to reduce platform-to-platform
+-- variation in results.
+SET extra_float_digits = -1;
 CREATE TABLE CIRCLE_TBL (f1 circle);
 INSERT INTO CIRCLE_TBL VALUES ('<(5,1),3>');
 INSERT INTO CIRCLE_TBL VALUES ('<(1,2),100>');
@@ -113,12 +114,12 @@ SELECT '' as five, c1.f1 AS one, c2.f1 AS two, (c1.f1 <-> c2.f1) AS distance
  five |      one       |      two       |     distance     
 ------+----------------+----------------+------------------
       | <(3,5),0>      | <(1,2),3>      | 0.60555127546399
-      | <(3,5),0>      | <(5,1),3>      | 1.47213595499958
+      | <(3,5),0>      | <(5,1),3>      |  1.4721359549996
       | <(100,200),10> | <(100,1),115>  |               74
-      | <(100,200),10> | <(1,2),100>    | 111.370729772479
-      | <(1,3),5>      | <(100,200),10> | 205.476756144497
+      | <(100,200),10> | <(1,2),100>    |  111.37072977248
+      | <(1,3),5>      | <(100,200),10> |   205.4767561445
       | <(5,1),3>      | <(100,200),10> |  207.51303816328
-      | <(3,5),0>      | <(100,200),10> | 207.793480159531
-      | <(1,2),3>      | <(100,200),10> | 208.370729772479
+      | <(3,5),0>      | <(100,200),10> |  207.79348015953
+      | <(1,2),3>      | <(100,200),10> |  208.37072977248
 (8 rows)
 

src/test/regress/sql/circle.sql

@@ -2,8 +2,9 @@
 -- CIRCLE
 --
 
--- avoid bit-exact output here because operations may not be bit-exact.
-SET extra_float_digits = 0;
+-- Back off displayed precision a little bit to reduce platform-to-platform
+-- variation in results.
+SET extra_float_digits = -1;
 
 CREATE TABLE CIRCLE_TBL (f1 circle);