FreeBSD: Install Cap'n Proto package

Required since bitcoin/bitcoin#31802 was merged.

Author: hebasto

.github/workflows/netbsd.yml

@@ -48,7 +48,7 @@ jobs:
           envs: 'CCACHE_COMPILERCHECK CCACHE_DIR CCACHE_MAXSIZE'
           prepare: |
             /usr/sbin/pkg_info > packages_before
-            /usr/sbin/pkg_add cmake git-base gcc14 pkg-config ccache boost libevent sqlite3 zeromq python313 py313-zmq
+            /usr/sbin/pkg_add cmake git-base gcc14 pkg-config ccache boost libevent sqlite3 capnproto zeromq python313 py313-zmq
             /usr/sbin/pkg_info > packages_after
             diff -w packages_before packages_after | grep '^>'
           run: git config --global --add safe.directory ${{ github.workspace }}