Do not update packages on FreeBSD (CI) (elixir-lang#9881)

FreeBSD builds are failing because `pkg` refuses to install 
new packages that were built using more recent OS versions. 

The build does not update the packages to avoid the error.

.cirrus.yml

@@ -143,7 +143,6 @@ test_freebsd_task:
     LC_ALL: en_US.UTF-8
 
   install_script:
-    - sudo pkg update
     - pkg install -y erlang git gmake
     - rm -rf .git
     - gmake compile