ci: add missing package installs for pyQuil pytest compatibility check

.github/workflows/validate-downstream.yml

@@ -30,7 +30,7 @@ jobs:
       - name: Setup pyQuil Repository
         run: |
           pip uninstall -y -r <(pip freeze) || true
-          pip install "./pyquil[latex]" maturin mypy ruff pytest pytest-mock
+          pip install "./pyquil[latex]" maturin mypy ruff pytest pytest-mock syrupy flaky respx
           maturin develop -m quil-rs/quil-py/Cargo.toml
 
       - name: Run mypy