Enable backtraces in turbopack integration tests (#89935)
## Enable Rust backtraces in CI tests
### What?
Added `RUST_BACKTRACE=1` environment variable to all Turbopack-related test workflows.
### Why?
This change enables detailed Rust backtraces when Turbopack encounters errors during CI tests, making it easier to diagnose and fix issues that occur in the Rust components.
Notably, some assertions/panics are about detecting race conditions, e.g.
```
thread 'tokio-runtime-worker' (1056161) panicked at turbopack/crates/turbo-tasks-backend/src/backend/operation/mod.rs:426:13:
Concurrent task lock acquisition detected. This is not allowed and indicates a bug. It can lead to deadlocks.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```
Rather than painfully attempting to reproduce locally we can just run with the env var all the time and perhaps that will be enough to figure out rare issues
