Add FreeTDS 1.5.21 to debian13

Build the static client libraries (libsybdb, libct) from the official
release tarball with OpenSSL; ODBC, the command-line apps, server and
pool are disabled.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

fetch-sources.sh

@@ -166,3 +166,5 @@ fetch sqlite-autoconf-3540100.tar.gz \
     https://www.sqlite.org/2026/sqlite-autoconf-3540100.tar.gz
 fetch wireguard-tools-v1.0.20260223.tar.xz \
     https://git.zx2c4.com/wireguard-tools/snapshot/wireguard-tools-v1.0.20260223.tar.xz
+fetch freetds-1.5.21.tar.gz \
+    https://www.freetds.org/files/stable/freetds-1.5.21.tar.gz