Add ubuntu to the matrix.

Author: brass75

.github/workflows/test.yml

@@ -31,7 +31,7 @@ jobs:
     strategy:
       matrix:
         python-version: ["3.10", "3.11", "3.12", "3.13"]
-        os: [ windows-latest, macos-latest ]
+        os: [ windows-latest, macos-latest, ubuntu-latest ]
       fail-fast: true
     runs-on: ${{ matrix.os }}
     steps: