ci: run Python 3.8 and 3.9 jobs on ubuntu-24.04

GitHub is rolling out Ubuntu 26.04 as `ubuntu-latest` gradually
across repositories, from 2026-10-19 through 2026-11-19 (see
actions/runner-images#14748). This
repository now receives it: on 2026-10-25, jobs started at 10:06 UTC
got the `ubuntu-24.04` image, and jobs started at 13:33 UTC got
`ubuntu-26.04`.

`actions/setup-python` takes its interpreters from the
`actions/python-versions` manifest, which has Linux x64 builds of
Python 3.8 and 3.9 for Ubuntu 24.04 but none for 26.04. The lowest
version it has for 26.04 is 3.10. So on 26.04, `setup-python` fails
with "The version '3.8' with architecture 'x64' was not found for
Ubuntu 26.04" (and likewise for 3.9). This broke six jobs:

- `test (smmap, 3.8)`, `test (smmap, 3.9)`, `test (gitdb, 3.8)`, and
  `test (gitdb, 3.9)` in `dependencies.yml`, which test the vendored
  `smmap` and `gitdb` packages (both declare `python_requires=">=3.7"`).
- `install/import (ubuntu-latest, 3.8)` and
  `install/import (ubuntu-latest, 3.9)` in `pythonpackage.yml`, which
  check that GitPython (`requires-python = ">=3.8"`) still installs
  and imports on those versions.

Run just those Ubuntu jobs on `ubuntu-24.04`. Everything else,
including the 3.10 jobs in the same matrices, stays on `ubuntu-latest`.
In `dependencies.yml`, `include` adds an `os` key only to the 3.8 and
3.9 combinations, and `runs-on` falls back to `ubuntu-latest` where it
is unset. In `pythonpackage.yml`, the `ubuntu-latest` 3.8 and 3.9
combinations are swapped for `ubuntu-24.04` ones, so the job names
show the image they actually run on. No status checks are required on
`main`, so the renamed jobs do not affect merging.

Python 3.8 and 3.9 can be installed on 26.04 in other ways: the
deadsnakes PPA publishes 3.8.20 and 3.9.25 for 26.04, and uv can
install python-build-standalone builds. But these would add a
different installation mechanism (and, for deadsnakes, a third-party
apt source) for just these jobs, while pinning keeps the same
`setup-python` builds that were tested before. This needs revisiting
when GitHub retires the `ubuntu-24.04` image, if 3.8 and 3.9 are still
tested then.

`actionlint` reports no problems with either workflow.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: EliahKagan

.github/workflows/dependencies.yml

@@ -11,12 +11,18 @@ permissions:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os || 'ubuntu-latest' }}
     strategy:
       fail-fast: false
       matrix:
         project: [smmap, gitdb]
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "3.13t"]
+        include:
+        # setup-python has no builds of these versions for Ubuntu 26.04.
+        - python-version: "3.8"
+          os: ubuntu-24.04
+        - python-version: "3.9"
+          os: ubuntu-24.04
 
     steps:
     - uses: actions/checkout@v7

.github/workflows/pythonpackage.yml

@@ -251,6 +251,17 @@ jobs:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
         python: ["3.8", "3.9", "3.10"]
+        exclude:
+        # setup-python has no builds of these versions for Ubuntu 26.04.
+        - os: ubuntu-latest
+          python: "3.8"
+        - os: ubuntu-latest
+          python: "3.9"
+        include:
+        - os: ubuntu-24.04
+          python: "3.8"
+        - os: ubuntu-24.04
+          python: "3.9"
     env:
       GIT_PYTHON_BACKEND: cli
     steps: