.cirrus.yml: skip pkg update for FreeBSD 13.1 (#12767)

diff --git a/.cirrus.yml b/.cirrus.yml
index 8e764ae..cfe1d8e 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -13,7 +13,6 @@
         image_family: freebsd-12-4
   timeout_in: 20m
   install_script:
-    - pkg update -f
     - pkg install -y gettext
   build_script:
     - NPROC=$(getconf _NPROCESSORS_ONLN)