gh-138158: Use the "data" tarfile extraction filter in Tools/ssl/multissltests.py (#138147)

The `Tools/ssl/multissltests.py` script may extract a possibly untrusted tarball.
Since the script does not necessarily use Python 3.14 or later (where the `"data"`
filter became the default `tarfile` extraction filter), the user may theoretically
suffer from a path traversal attack.

Although the script should not be used in production and usually relies on downloading
trusted sources, the `"data"` extraction filter is now explicitly used wherever relevant.

Author: ParzivalHack

Tools/ssl/multissltests.py

@@ -306,7 +306,7 @@ def _unpack_src(self):
                 raise ValueError(member.name, base)
             member.name = member.name[len(base):].lstrip('/')
         log.info("Unpacking files to {}".format(self.build_dir))
-        tf.extractall(self.build_dir, members)
+        tf.extractall(self.build_dir, members, filter='data')
 
     def _build_src(self, config_args=()):
         """Now build openssl"""