Update OS matrix in smoke test

This adds more explicit Ubuntu variants + Windows 2025

Author: tianon

.github/workflows/ci.yml

@@ -14,7 +14,13 @@ jobs:
   build-matrix:
     strategy:
       matrix:
-        os: [ ubuntu-latest, windows-2019, windows-2022 ]
+        os:
+          - ubuntu-24.04
+          - ubuntu-22.04
+          - ubuntu-20.04
+          - windows-2025
+          - windows-2022
+          - windows-2019
     name: Build ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     steps: