Move Windows CI to the windows-2025-vs2026 runner (#64)

GitHub is redirecting `windows-2025` runner requests to
`windows-2025-vs2026` by 2026-06-15. Move on our own schedule rather
than being silently redirected.

Also bump the actionlint CI image to 20260529, whose actionlint knows
the `windows-2025-vs2026` label so workflow linting still passes.

Author: SeanTAllen

.github/workflows/breakage-against-windows-ponyc-latest.yml

@@ -10,7 +10,7 @@ permissions:
 jobs:
   windows:
     name: Verify main against the latest ponyc on Windows
-    runs-on: windows-2025
+    runs-on: windows-2025-vs2026
     steps:
       - name: Disable Windows Defender
         run: Set-MpPreference -DisableRealtimeMonitoring $true

.github/workflows/lint-action-workflows.yml

@@ -17,6 +17,6 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v6.0.2
       - name: Check workflow files
-        uses: docker://ghcr.io/ponylang/shared-docker-ci-actionlint:20260311
+        uses: docker://ghcr.io/ponylang/shared-docker-ci-actionlint:20260529
         with:
           args: -color

.github/workflows/pr.yml

@@ -69,7 +69,7 @@ jobs:
 
   test-x86-64-windows-vs-ponyc-release:
     name: Windows x86-64 (LibreSSL) with most recent ponyc release
-    runs-on: windows-2025
+    runs-on: windows-2025-vs2026
     steps:
       - name: Disable Windows Defender
         run: Set-MpPreference -DisableRealtimeMonitoring $true