fix(ci): reduce test parallelism on Windows to prevent disk exhaustion

Use -p 1 on Windows to run one package at a time, reducing disk pressure
from accumulated build artifacts. Other platforms use default parallelism.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: fansenze

.github/workflows/ci.yml

@@ -73,9 +73,15 @@ jobs:
           Write-Host "Disk space after cleanup:"
           Get-PSDrive C | Select-Object Used,Free | Format-Table
 
-      - name: Unit Test
+      - name: Unit Test (Windows)
+        if: runner.os == 'Windows'
+        run: |
+          go test -parallel 4 -p 1 ./internal/...
+
+      - name: Unit Test (Non-Windows)
+        if: runner.os != 'Windows'
         run: |
-          go test -parallel 4 -p 2 ./internal/...
+          go test -parallel 4 ./internal/...
   lint:
     name: Lint&Check
     runs-on: rspack-ubuntu-22.04-large