test(tracing): allow tracer init to fail

[shekhirin]

Thanks @Rjected for pointing out

failures:

---- cli::tests::override_trusted_setup_file stdout ----
thread 'cli::tests::override_trusted_setup_file' panicked at /Users/shekhirin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tracing-subscriber-0.3.18/src/util.rs:91:14:
failed to set global default subscriber: SetGlobalDefaultError("a global default trace dispatcher has already been set")
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[Rjected]

lgtm!