[Chore] Lint services/tunnelbroker/CMakeLists.txt

Summary: Lint tunnelbroker's cmake

Test Plan:

nix develop
cmake-lint services/backup/CMakeLists.txt

Reviewers: atul, varun, max, karol

Reviewed By: atul

Subscribers: ashoat, tomek, adrian, abosh

Differential Revision: https://phab.comm.dev/D4566