ci: add flask dependency to PyInstaller workflow

Add flask to test dependencies in PyInstaller workflow to support
integration tests that use the mock NITRO API server.

Author: slauger

.github/workflows/pyinstaller.yml

@@ -32,7 +32,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install -e .
-        pip install ruff black mypy types-requests pytest
+        pip install ruff black mypy types-requests pytest flask
 
     - name: Run ruff (linting)
       run: |