FreeBSD CI: also perform test on 11.3-STABLE

The official guide [1] says 11.3-RELEASE doesn't boot properly so
using 11.3-STABLE instead.

[1] https://cirrus-ci.org/guide/FreeBSD/

.cirrus.yml

@@ -11,3 +11,18 @@ FreeBSD_task:
     - make -j $(sysctl -n hw.ncpu || echo 4) -C tmp
     - ldd build/vpnserver
     - build/vpncmd /tool /cmd:check
+
+FreeBSD_task:
+  freebsd_instance:
+    # 11-3-release doesn't boot: https://cirrus-ci.org/guide/FreeBSD/
+    image: freebsd-11-3-stable-amd64-v20191205
+  env:
+    ASSUME_ALWAYS_YES: TRUE # required for unattanded "pkg" invocation
+  install_script:
+    - pkg install cmake openssl111 git
+    - git submodule update --init --recursive
+  script:
+    - ./configure
+    - make -j $(sysctl -n hw.ncpu || echo 4) -C tmp
+    - ldd build/vpnserver
+    - build/vpncmd /tool /cmd:check