docker, actions: Update for Ubuntu 24.04 (#39548)

GitHub is preparing to roll out Ubuntu 24.04 to Actions. This prepares
us for that.

* Update our own Docker development environment to be based on 24.04.
* `svn` has been removed from the default Actions image. Install it
  manually where needed.

.github/files/gh-wp-svn-autopublish/workflows/wp-svn-autopublish.yml

@@ -31,6 +31,9 @@ jobs:
           fi
           exit $EXIT
 
+      - name: Install svn
+        run: command -v svn || sudo apt-get install -y subversion
+
       - uses: actions/checkout@v4
         with:
           path: src

tools/docker/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:22.04
+FROM ubuntu:24.04
 
 VOLUME ["/var/www/html"]