Unstable select_parallel regression output in 12rc1

Building the 12rc1 package on Ubuntu eoan/amd64, I got this
regression diff:

12:06:27 diff -U3 /<<PKGBUILDDIR>>/build/../src/test/regress/expected/select_parallel.out /<<PKGBUILDDIR>>/build/src/bin/pg_upgrade/tmp_check/regress/results/select_parallel.out
12:06:27 --- /<<PKGBUILDDIR>>/build/../src/test/regress/expected/select_parallel.out 2019-09-23 20:24:42.000000000 +0000
12:06:27 +++ /<<PKGBUILDDIR>>/build/src/bin/pg_upgrade/tmp_check/regress/results/select_parallel.out 2019-09-26 10:06:21.171683801 +0000
12:06:27 @@ -21,8 +21,8 @@
12:06:27 Workers Planned: 3
12:06:27 -> Partial Aggregate
12:06:27 -> Parallel Append
12:06:27 - -> Parallel Seq Scan on d_star
12:06:27 -> Parallel Seq Scan on f_star
12:06:27 + -> Parallel Seq Scan on d_star
12:06:27 -> Parallel Seq Scan on e_star
12:06:27 -> Parallel Seq Scan on b_star
12:06:27 -> Parallel Seq Scan on c_star
12:06:27 @@ -75,8 +75,8 @@
12:06:27 Workers Planned: 3
12:06:27 -> Partial Aggregate
12:06:27 -> Parallel Append
12:06:27 - -> Seq Scan on d_star
12:06:27 -> Seq Scan on f_star
12:06:27 + -> Seq Scan on d_star
12:06:27 -> Seq Scan on e_star
12:06:27 -> Seq Scan on b_star
12:06:27 -> Seq Scan on c_star
12:06:27 @@ -103,7 +103,7 @@
12:06:27 -----------------------------------------------------
12:06:27 Finalize Aggregate
12:06:27 -> Gather
12:06:27 - Workers Planned: 1
12:06:27 + Workers Planned: 3
12:06:27 -> Partial Aggregate
12:06:27 -> Append
12:06:27 -> Parallel Seq Scan on a_star

Retriggering the build worked, though.

Christoph