ci(windows-e2e): run the e2e-windows job on windows-latest-32-core

Same runner class as the os-tests Windows row. Seven files run in
parallel, each spawning process trees; measured on the fixed suite the
test step drops from 153-171 s to 124 s and the job from ~5 min to 3.1.

.github/workflows/tests-os.yml

@@ -194,7 +194,10 @@ jobs:
     # Windows race that passes on retry is still a race. Tracked Windows bugs are strict
     # xfails (per-file KNOWN tables), so a fix turns this job red until the entry goes.
     name: Windows E2E (real processes)
-    runs-on: windows-latest
+    # 32-core like os-tests' Windows row: seven files run in parallel and each spawns
+    # process trees; on the 4-vCPU image the suite step took 153-171 s (job 4.7-5.6 min),
+    # here 124 s (job 3.1 min), with headroom against scheduling-starved timeouts.
+    runs-on: windows-latest-32-core
     timeout-minutes: 25
     steps:
       - name: Checkout code