fix(ci): don't --rm the boot-test VM — it races serial.log capture

CodeRabbit review: with --rm, a VM that exits early (the exact failure
M0 exists to diagnose) is autoremoved before cleanup() reads podman
logs, silently losing the serial console. cleanup() already does the
explicit rm -f.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018bGymcRkVtV7DPToWDjZyZ

Author: hanthor

.github/workflows/boot-test-aarch64.yml

@@ -134,7 +134,10 @@ jobs:
           trap cleanup EXIT
 
           echo "==> Launching ephemeral VM from ${IMAGE}..."
-          sudo "$HOME/.cargo/bin/bcvk" ephemeral run -d --rm -K --console \
+          # No --rm: if the VM exits early (the exact failure we want to
+          # diagnose), autoremoval would race away the container before
+          # cleanup() captures serial.log. cleanup() does the rm -f.
+          sudo "$HOME/.cargo/bin/bcvk" ephemeral run -d -K --console \
             --memory 8192M --vcpus 4 --name "$VM_NAME" "${IMAGE}"
 
           echo "==> Waiting for SSH (timeout ${SSH_TIMEOUT}s)..."