CI: Use ubuntu-22.04 to support Python 3.7

Author: amotl

.github/workflows/tests.yml

@@ -24,8 +24,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: ["ubuntu-latest"]
         python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
+        os: ["ubuntu-22.04"]
         cratedb-version: ["nightly"]
       fail-fast: false