Re-adhere to policy of no more than 20 tests per parallel group.

As explained at the head of parallel_schedule, we place an arbitrary limit
of 20 test cases per parallel group.  Commit c7a9fa399 overlooked this.

Least messy solution seems to be to move the "comments" test to the next
group, since it doesn't really belong in a group of datatype tests anyway.

src/test/regress/parallel_schedule

@@ -23,14 +23,14 @@ test: numerology
 # ----------
 # The second group of parallel tests
 # ----------
-test: point lseg line box path polygon circle date time timetz timestamp timestamptz interval abstime reltime tinterval inet macaddr macaddr8 tstypes comments
+test: point lseg line box path polygon circle date time timetz timestamp timestamptz interval abstime reltime tinterval inet macaddr macaddr8 tstypes
 
 # ----------
 # Another group of parallel tests
 # geometry depends on point, lseg, box, path, polygon and circle
 # horology depends on interval, timetz, timestamp, timestamptz, reltime and abstime
 # ----------
-test: geometry horology regex oidjoins type_sanity opr_sanity expressions
+test: geometry horology regex oidjoins type_sanity opr_sanity comments expressions
 
 # ----------
 # These four each depend on the previous one

src/test/regress/serial_schedule

@@ -43,13 +43,13 @@ test: inet
 test: macaddr
 test: macaddr8
 test: tstypes
-test: comments
 test: geometry
 test: horology
 test: regex
 test: oidjoins
 test: type_sanity
 test: opr_sanity
+test: comments
 test: expressions
 test: insert
 test: insert_conflict