Fix CI: Install subversion for Ubuntu CI workers

- Add subversion to the Ubuntu dependency installation step in CI
- This fixes the failing test_ensure_svn_available test which expects
  SVN to be available in CI environment
- Addresses test failure in ubuntu-latest CI workers

Co-authored-by: notatallshaw <[email protected]>

Author: Copilot

.github/workflows/ci.yml

@@ -135,7 +135,7 @@ jobs:
         if: startsWith(matrix.os, 'ubuntu-')
         run: |
           sudo apt-get update
-          sudo apt-get install bzr
+          sudo apt-get install bzr subversion
 
       - name: Install MacOS dependencies
         if: runner.os == 'macOS'