ci: qualify HTTP on pinned macOS and Windows runners

Author: Philip Z

.github/workflows/http-platforms.yml

@@ -34,7 +34,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [macos-latest, windows-latest]
+        os: [macos-26, macos-26-intel, windows-2025]
     defaults:
       run:
         shell: bash