build: Exempt syn 2.0.114

It seems like everyone just decides to trust or exempt this crate. There
are a few "safe-to-run" audits but no one really commits to an audit
certifying "safe-to-deploy". I'm not content with this, but I definitely
need way more time if I'm going to actually audit the whole thing. So
for now, an exemption is preferred over "trusting" since it keeps the
audit in my backlog.

Signed-off-by: hashcatHitman <155700084+hashcatHitman@users.noreply.github.com>

Author: hashcatHitman

supply-chain/config.toml

@@ -28,3 +28,7 @@ criteria = "safe-to-deploy"
 [[exemptions.regex-automata]]
 version = "0.4.13"
 criteria = "safe-to-deploy"
+
+[[exemptions.syn]]
+version = "2.0.114"
+criteria = "safe-to-deploy"