Fix highlighting for rust raw byte string literals

[nico-abram]

Here's an example of what this should fix: https://doc.rust-lang.org/reference/tokens.html?highlight=raw%20string#raw-byte-string-literals

[joshgoebel]

Thanks so much!

Please add markup tests to test/markup/rust/strings, etc to verify this new behavior.

[nico-abram]

Thanks so much!

Please add markup tests to test/markup/rust/strings, etc to verify this new behavior.

Done @joshgoebel

[nico-abram]

Sorry, I forgot to update the expect file, just pushed again

[joshgoebel]

Perfect. Can you add changlog entry I don't think I saw it.

[nico-abram]

Added changelog entry

[joshgoebel]

@nico-abram Thanks so much for the contribution!