canvas scrollbar not visible on page when scrolling

Description
when scrolling a canvas control on a page the scrollbar is not visible. Therefore, scrolling happens one mouse wheel at a time instead of the option to slide the scrollbar.

Code example to reproduce the issue:

import flet as ft
import flet.canvas as cv

md1 = """
# Markdown Example
Markdown allows you to easily include formatted text, images, and even formatted Dart code in your app.

## Titles

Setext-style

This is an H1
=============

This is an H2
-------------

Atx-style

# This is an H1

## This is an H2

###### This is an H6

Select the valid headers:

- [x] `# hello`
- [ ] `#hello`

## Links

[Google](https://www.google.com)

## Images

![Image from Flet assets](/icons/icon-192.png)

![Test image](https://picsum.photos/200/300)

## Tables

|Syntax                                 |Result                               |
|---------------------------------------|-------------------------------------|
|`*italic 1*`                           |*italic 1*                           |
|`_italic 2_`                           | _italic 2_                          |
|`**bold 1**`                           |**bold 1**                           |
|`__bold 2__`                           |__bold 2__                           |
|`This is a ~~strikethrough~~`          |This is a ~~strikethrough~~          |
|`***italic bold 1***`                  |***italic bold 1***                  |
|`___italic bold 2___`                  |___italic bold 2___                  |
|`***~~italic bold strikethrough 1~~***`|***~~italic bold strikethrough 1~~***|
|`~~***italic bold strikethrough 2***~~`|~~***italic bold strikethrough 2***~~|

## Styling

Style text as _italic_, __bold__, ~~strikethrough~~, or `inline code`.

- Use bulleted lists
- To better clarify
- Your points

## Code blocks

Formatted Dart code looks really pretty too:

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      body: ft.Markdown(data: markdownData),
    ),
  ));
}
"""

def main(page: ft.Page):
    page.theme_mode = ft.ThemeMode.DARK
    page.scroll = "ALWAYS"

    can =  cv.Text(
                0,
                0,
                md1
             )

    cp = cv.Canvas(
        [ can ],
        width=float("inf"),
        expand=True
    )

    page.add(cp)

ft.app(main)

Describe the results you received:
when scrolling a canvas control on a page the scrollbar is not visible.

Describe the results you expected:
a visible scrollbar when scrolling a canvas control on a page.

Additional information you deem important (e.g. issue happens only occasionally):

Flet version (pip show flet):

Name: flet
Version: 0.7.4
Summary: Flet for Python - easily build interactive multi-platform apps in Python
Home-page: 
Author: Appveyor Systems Inc.
Author-email: hello@flet.dev
License: Apache-2.0
Location: /home/george/dev/flet/venv/lib/python3.11/site-packages
Requires: flet-core, httpx, oauthlib, packaging, watchdog, websocket-client, websockets
Required-by: flet-material

Operating system:
Ubuntu Linux 23.04.

Additional environment details:

Run the provided Python reproduction with Flet 0.7.4 on Ubuntu Linux 23.04 and confirm whether the canvas scrollbar is absent while page scrolling. Trace the canvas and page scrolling behavior, then verify that a visible scrollbar supports sliding through the canvas content rather than only mouse-wheel steps.