Fix CI backend-tests failing to collect FTP test suite

CI only installed requirements.txt, missing pyOpenSSL from
requirements-dev.txt. This caused an ImportError on
TLS_FTPHandler during test collection, blocking all
unit/services tests. Also adds pytest-timeout to dev deps
instead of ad-hoc pip install in CI.

.github/workflows/ci.yml

@@ -96,7 +96,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install -r requirements.txt
-          pip install pytest pytest-asyncio pytest-cov pytest-timeout
+          pip install -r requirements-dev.txt
 
       - name: Run tests
         timeout-minutes: 10