ci: allow FreeBSD jobs to fail

The FreeBSD CI is flaky.

The CI is of only limited use if it fails spuriously. Until a glorious
future where GLib has active FreeBSD developers eager to debug its
testsuite, it would be pragmatic to accept the CI run as passing if all
other platforms are happy.
13 jobs for mcatanzaro/sorry-freebsd in 15 minutes and 17 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Style Check
passed #1342436
check-todos

00:02:04

passed #1342435
style-check-diff

00:02:21

 
  Build
passed #1342439
cross-android_api21_arm64

00:00:57

passed #1342440
cross-android_api28_arm64

00:01:09

passed #1342441
cross-mingw64

00:01:27

passed #1342438
debian-stable-x86_64

00:02:46

passed #1342437
fedora-x86_64

00:09:00

passed #1342444
freebsd-11
freebsd-11-x86_64

00:05:10

passed #1342445
freebsd-12
freebsd-12-x86_64

00:04:39

passed #1342446
macos
macos

00:04:16

passed #1342442
win32-ps
msys2-mingw32

00:13:56

passed #1342443
win32-ps
vs2017-x64

00:08:09

 
  Coverage
passed #1342447
coverage

00:01:19

76.2%