[services] Tunnelbroker - Update Cargo dependencies with the CXX

Summary:
This small diff introduces updating Cargo dependencies with the CXX to avoid using unsafe.

Related Linear task: ENG-1438

Test Plan: Successfully run cargo build inside the services/tunnelbroker/rust-notifications folder.

Reviewers: karol, varun, tomek, jon, ashoat

Reviewed By: tomek, ashoat

Subscribers: ashoat, tomek, adrian, atul, karol, abosh

Differential Revision: https://phab.comm.dev/D4803