BUILD: cirrus-ci: suppress OS version check when installing packages

since we run "snapshot" images of FreeBSD, it is possible that kernel
ABI version might change from time to time. It might differ from
prebuilt packages (installed via "pkg"). We do not test kernel modules,
so for us is safe to ignore ABI mismatch.

.cirrus.yml

@@ -5,6 +5,8 @@ FreeBSD_task:
       image_family: freebsd-12-1-snap
       image_family: freebsd-11-3-snap
   only_if: $CIRRUS_BRANCH =~ 'master|next'
+  env:
+    IGNORE_OSVERSION: yes # supress package installation error on FreeBSD-13
   install_script:
     - pkg update -f && pkg upgrade -y && pkg install -y openssl git gmake lua53 socat
   script: