ci(devcontainer): only skip cross-device test, not fs-errors

The fs_errors test works fine in Codespaces where the user is non-root.
It only fails in our current CI environment because we run as root.

https://claude.ai/code/session_01LfpnUZrgq93MVZgA3KVqE6

Author: claude

.devcontainer/devcontainer.json

@@ -2,7 +2,7 @@
   "name": "parallel-disk-usage (Rust only)",
   "image": "mcr.microsoft.com/devcontainers/rust:1",
   "remoteEnv": {
-    "RUSTFLAGS": "--cfg pdu_test_skip_cross_device --cfg pdu_test_skip_fs_errors"
+    "RUSTFLAGS": "--cfg pdu_test_skip_cross_device"
   },
   "customizations": {
     "vscode": {

.devcontainer/full/devcontainer.json

@@ -2,7 +2,7 @@
   "name": "parallel-disk-usage (full)",
   "image": "mcr.microsoft.com/devcontainers/rust:1",
   "remoteEnv": {
-    "RUSTFLAGS": "--cfg pdu_test_skip_cross_device --cfg pdu_test_skip_fs_errors"
+    "RUSTFLAGS": "--cfg pdu_test_skip_cross_device"
   },
   "features": {
     "ghcr.io/devcontainers/features/node:1": {