install: Support Debian 13.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

.github/workflows/production-suite.yml

@@ -154,6 +154,11 @@ jobs:
             os: bookworm
             extra-args: --test-custom-db
 
+          - docker_image: zulip/ci:trixie
+            name: Debian 13 production install
+            os: trixie
+            extra-args: ""
+
     name: ${{ matrix.name  }}
     container:
       image: ${{ matrix.docker_image }}

.github/workflows/zulip-ci.yml

@@ -28,7 +28,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          # Base images are built using `tools/ci/Dockerfile.prod.template`.
+          # Base images are built using `tools/ci/Dockerfile`.
           # The comments at the top explain how to build and upload these images.
           # Ubuntu 22.04 ships with Python 3.10.12.
           - docker_image: zulip/ci:jammy
@@ -48,6 +48,12 @@ jobs:
             os: noble
             include_documentation_tests: false
             include_frontend_tests: false
+          # Debian 13 ships with Python 3.13.5.
+          - docker_image: zulip/ci:trixie
+            name: Debian 13 (Python 3.13, backend)
+            os: trixie
+            include_documentation_tests: false
+            include_frontend_tests: false
 
     runs-on: ubuntu-latest
     name: ${{ matrix.name }}