Improvements to the development environment (#383)

* Update Home Assistant dev version in requirements_dev.txt

* Avoid "Error starting FFmpeg" error in VSCode dev container logs

* Add "editor.formatOnSaveMode": "modifications" to .vscode/settings.json

.vscode/settings.json

@@ -1,7 +1,8 @@
 {
     "[python]": {
         "editor.defaultFormatter": "ms-python.black-formatter",
-        "editor.formatOnSave": true
+        "editor.formatOnSave": true,
+        "editor.formatOnSaveMode": "modifications"
     },
     "pylint.lintOnChange": false,
     "files.associations": {