Fedora 33: reduce concurrency

... to avoid OOM. E.g.:

as: out of memory allocating 4064 bytes after a total of 396447744 bytes
29 jobs for 2.12.4-1 in 36 minutes and 51 seconds (queued for 5 seconds)
latest
Status Name Job ID Coverage
  Build
passed build/centos/7 #104479
docker

00:09:07

passed build/centos/8 #104478
docker

00:07:18

passed build/fedora/33 #104481
docker

00:17:19

passed build/fedora/34 #104480
docker

00:16:16

passed build/opensuse/15.2 #104484
docker

00:09:51

passed build/sles/12.5 #104483
docker

00:14:56

passed build/sles/15.2 #104501
docker

00:15:39

canceled build/sles/15.2 #104482
docker

00:12:45

 
  Test
passed test/centos/7 #104486
docker

00:01:15

passed test/centos/8 #104485
docker

00:00:42

passed test/fedora/33 #104488
docker

00:01:30

passed test/fedora/34 #104487
docker

00:01:23

passed test/opensuse/15.2 #104491
docker

00:02:27

passed test/sles/12.5 #104490
docker

00:02:49

passed test/sles/15.2 #104489
docker

00:03:05

 
  Upload
passed upload/SUSE/12.5 #104524
docker

00:00:18

passed upload/SUSE/15.2 #104525
docker

00:00:18

passed upload/epel/7 #104526
docker

00:00:18

passed upload/epel/8 #104527
docker

00:00:23

passed upload/fedora/33 #104528
docker

00:00:23

passed upload/fedora/34 #104529
docker

00:00:21

passed upload/openSUSE/15.2 #104530
docker

00:00:19

canceled upload/SUSE/12.5 #104497
docker

canceled upload/SUSE/15.2 #104496
docker

canceled upload/epel/7 #104493
docker

canceled upload/epel/8 #104492
docker

canceled upload/fedora/33 #104495
docker

canceled upload/fedora/34 #104494
docker

canceled upload/openSUSE/15.2 #104498
docker