Switch to ubuntu-22.04 for CI tests

An issue with oscrypto means it currently does not work on 24.04. Ref: wbond/oscrypto#78 (comment)

Author: pjrobertson

.github/workflows/tests-core.yaml

@@ -11,7 +11,7 @@ on:
 
 jobs:
   tests:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
         python-version: ["3.10", "3.11", "3.12"]

.github/workflows/tests-download.yaml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   tests:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
         python-version: ["3.10"] # only run expensive downloads on one (lowest) python version