github: Enable Rust backtraces for tests

Author: penberg

.github/workflows/rust.yml

@@ -23,6 +23,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Run Checks
     env:
+      RUST_BACKTRACE: 1
       RUSTFLAGS: -D warnings --cfg tokio_unstable
     steps:
       - uses: hecrj/setup-rust-action@v2
@@ -179,6 +180,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Run Tests
     env:
+      RUST_BACKTRACE: 1
       RUSTFLAGS: -D warnings --cfg tokio_unstable
     steps:
     - uses: hecrj/setup-rust-action@v2