ci: bump Python to 3.9 at `install-deps-freebsd`

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci

.github/actions/install-deps-freebsd/action.yml

@@ -14,11 +14,11 @@ runs:
           ninja \
           icu \
           libiconv \
-          python38 \
+          python39 \
           autoconf \
           automake \
           libtool
 
-        which python3 || ln -s /usr/local/bin/python3.8 /usr/local/bin/python3
+        which python3 || ln -s /usr/local/bin/python3.9 /usr/local/bin/python3
         python3 -m pip -V || curl -fsSL ${PIP_URL} | python3
       shell: bash