[Rich text editor] Update list item bullet appearance

[jonnyandrew]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

Update the list item bullet appearance in the rich text editor.

Motivation and context

PSU-1063

Screenshots / GIFs

Before	After

Tests

• Enable the rich text editor in labs
• Start typing a message
• Tap the bullet list button
• Note the appearance of the bullets

Tested devices

• Physical
• Emulator
• OS version(s): Android 13

Checklist

• Changes has been tested on an Android device or Android emulator with API 21
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com./vector-im/element-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request includes a new file under ./changelog.d. See https://github.com./vector-im/element-android/blob/develop/CONTRIBUTING.md#changelog
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR
• If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()

[ElementBot]

	Warnings
⚠️	Please add a reviewer to your PR.

Generated by 🚫 dangerJS against b73eb1d

[ElementBot]

	Warnings
⚠️	Please add a reviewer to your PR.

Generated by 🚫 dangerJS against b73eb1d

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[bmarty]

LGTM