Bump bytemuck and update deny.toml for syn's move to unicode-ident.

[eddyb]

This is a prerequisite for:

• Minimally integrate SPIR-T (opt-in via RUSTGPU_CODEGEN_ARGS=--spirt). #940 (comment)
  ^{(the link goes to my comment explanation the plan that this PR is a part of)}

The bytemuck part is not even that interesting (I forget what needed it), but rather newer versions of syn switching from unicode-xid to unicode-ident, the latter of which requires allowing the Unicode-DFS-2016 license.

cc @repi @Jake-Shadle This is the Unicode license change I brought up in the past.