Test new mariadb versions with py3.8 only for now

The requirements files are compiled specifically for py3.8, so when
the system python is 3.12, the CI fails when trying to install
dependencies. Run the CI only on py3.8.

.github/workflows/ci.yml

@@ -24,16 +24,17 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.8, 3.12]
+        python-version: [3.8]
         backend: ["sqlite", "mariadb"]
         mariadb-version: ["10.4"]
-        # include:
-        #   - python-version: 3.12  # Possible future version.
-        #     backend: "mariadb"
-        #     mariadb-version: "10.5"
-        #   - python-version: 3.12  # Possible future version.
-        #     backend: "mariadb"
-        #     mariadb-version: "10.11"
+        include:
+          # Not sure yet how best to include CI for a newer python version with the pip-tools workflow.
+          - python-version: 3.8  # Possible future version.
+            backend: "mariadb"
+            mariadb-version: "10.5"
+          - python-version: 3.8  # Possible future version.
+            backend: "mariadb"
+            mariadb-version: "10.11"
 
     name: "py${{ matrix.python-version }}-${{ matrix.backend }}-${{ matrix.mariadb-version }}"