tools: update pkg in bsd-setup.

This circumvents a buggy pkg version in 11.x.
Move env var to the proper place while here.

Change-Id: Ib527a92cf8b542c8478daddf082c696caa296d80
Reviewed-on: https://code.wireshark.org/review/36055
Reviewed-by: Dario Lombardo <lomato@gmail.com>

.cirrus.yml

@@ -5,9 +5,12 @@ task:
       - image_family: freebsd-13-0-snap
       - image_family: freebsd-12-0
       - image_family: freebsd-11-3-snap
+  env:
+    ASSUME_ALWAYS_YES: YES
   setup_script:
-    - env ASSUME_ALWAYS_YES=YES pkg install bash
-    - env ASSUME_ALWAYS_YES=YES tools/bsd-setup.sh --install-optional
+    - pkg update -f
+    - pkg install bash
+    - tools/bsd-setup.sh --install-optional
   build_script:
     - mkdir build
     - cd build