test changes for 24.04 ubuntu github action migration

Explicitly test python 3.8 on ubunutu-22.04.

Explicitly test python 3.12 on ubuntu-24.04.

disable all other testing on 24.04 for now. In future commit, remove
explicit matrix.os list entry ubuntu-24.04 in favor of ubuntu-latest
and add 22.04 to exclude.os

[skip travis]

.github/workflows/ci-test.yml

@@ -55,7 +55,7 @@ jobs:
           - "3.13"
           # - 3.6 run via include on ubuntu 20.04
           # - "3.7"
-          - "3.8"
+          # - "3.8" run via include for ubuntu-22.04
           # - "3.9"
           - "3.10"
           - "3.11"
@@ -64,7 +64,8 @@ jobs:
         # use for multiple os or ubuntu versions
         #os: [ubuntu-latest, macos-latest, windows-latest]
         # ubuntu latest 22.04 12/2022
-        os: [ubuntu-latest, ubuntu-20.04]
+        # ubuntu latest 24.04 12/2024
+        os: [ubuntu-latest, ubuntu-22.04, ubuntu-20.04, ubuntu-24.04]
 
         # if the ones above fail. fail the build
         experimental: [ false ]
@@ -81,9 +82,18 @@ jobs:
             - python-version: 3.6
               os: ubuntu-20.04
 
+            # 3.8 not available on new 24.04 runners, so run on 22.04 ubuntu
+            - python-version: 3.8
+              os: ubuntu-22.04
+
+              # test on new default 24.04 runner 3.12 for 24.04
+            - python-version: 3.12
+              os: ubuntu-24.04
+
         exclude:
-            # skip all python versions on 20.04 except explicitly included
-            - os: ubuntu-20.04
+            # skip all python versions on 20.04/24.04 except
+            # explicitly included
+            - os: [ubuntu-20.04, ubuntu-24.04]
 
     # run the finalizer for coveralls even if one or more
     # experimental matrix runs fail.