update runner image for C tests

Author: paulbkoch

.github/workflows/ci.yml

@@ -405,22 +405,22 @@ jobs:
             existing: ""
             scheduled: ""
           - name: win_release_64
-            image: windows-latest
+            image: windows-2025-vs2026
             options: "-release_64"
             existing: "-existing_release_64"
             scheduled: "-analysis"
           - name: win_debug_64
-            image: windows-latest
+            image: windows-2025-vs2026
             options: "-debug_64"
             existing: "-existing_debug_64"
             scheduled: ""
           - name: win_release_32
-            image: windows-latest
+            image: windows-2025-vs2026
             options: "-release_32"
             existing: ""
             scheduled: "-analysis"
           - name: win_debug_32
-            image: windows-latest
+            image: windows-2025-vs2026
             options: "-debug_32"
             existing: ""
             scheduled: ""