Get Repo Root Panic

Panic in get_repo_root() when OpenTelemetry tracing is enabled with TRACEPARENT

Running terragrunt stack generate (or any command that invoked shell commands like git rev-parse) with OpenTelemetry trace exporting enabled (TG_TELEMETRY_TRACE_EXPORTER=http) caused a nil pointer panic:

Call to function "get_repo_root" failed: panic in function implementation:
runtime error: invalid memory address or nil pointer dereference

The root cause of the panic was fixed, and telemetry codepaths have been hardened against future panics.