[ci] Test multiple python versions.

python/base.yml

 variables:
   PIP_CACHE_DIR: "$CI_PROJECT_DIR/.cache/pip"
 
+# we test all released and supported versions
+# https://devguide.python.org/versions/#supported-versions
+.python-versions:
+  versions:
+    - "3.8"
+    - "3.9"
+    - "3.10"
+    - "3.11"
+
 .python-default:
-  image: python:3.8
+  image: python:$PYTHON_VERSIONS
   cache:
     paths:
       - .cache/pip
@@ -15,3 +24,6 @@ variables:
     when: on_failure
     paths:
       - "*.log"
+  parallel:
+    matrix:
+      - PYTHON_VERSIONS: !reference [.python-versions, versions]

test/python.yml

@@ -7,6 +7,7 @@ py_build:
     matrix:
       - PROJECT_ROOT: "test/python-template"
         EXIT_CODE: 0
+        PYTHON_VERSIONS: !reference [.python-versions, versions]
 
 py_tests:
   before_script:
@@ -20,9 +21,8 @@ py_tests:
   parallel:
     matrix:
       - PROJECT_ROOT: "test/python-template"
-        EXIT_CODE: 0
-      - PROJECT_ROOT: "test/python-template"
-        EXIT_CODE: 1
+        EXIT_CODE: [0, 1]
+        PYTHON_VERSIONS: !reference [.python-versions, versions]
   allow_failure:
     exit_codes: 1
 
@@ -35,3 +35,4 @@ py_lint:
     matrix:
       - PROJECT_ROOT: "test/python-template"
         EXIT_CODE: 0
+        PYTHON_VERSIONS: !reference [.python-versions, versions]