Switch to using latest Ubuntu (pymc-devs#7758)

Author: zaxtax

.github/workflows/tests.yml

@@ -54,7 +54,7 @@ jobs:
     if: ${{ needs.changes.outputs.changes == 'true' }}
     strategy:
       matrix:
-        os: [ubuntu-20.04]
+        os: [ubuntu-latest]
         floatx: [float64]
         python-version: ["3.13"]
         test-subset:
@@ -286,9 +286,9 @@ jobs:
     if: ${{ needs.changes.outputs.changes == 'true' }}
     strategy:
       matrix:
-        os: [ubuntu-20.04]
+        os: [ubuntu-latest]
         floatx: [float64]
-        python-version: ["3.12"]
+        python-version: ["3.13"]
         test-subset:
           - |
             tests/distributions/test_random_alternative_backends.py