Blogging Prompts Feature Introduction: update lightbulb icon

[ScoutHarris]

Ref: #18176
Depends on: #18304

The lightbulb Material icon is now used in the Blogging Prompts feature introduction header instead of the SF Symbol.

To test:

• Enable bloggingPrompts feature flag.
• Run the app.
• When the app launches, the Feature Introduction will appear.
• Verify the updated lightbulb icon is displayed.

Before	After

Regression Notes

1. Potential unintended areas of impact
   N/A

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   N/A

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

You can test the changes in Jetpack from this Pull Request by:

• Clicking here or scanning the QR code below
• Then installing the build number pr18320-e72e2fa from App Center on your iPhone

The .ipa file can also be downloaded directly here.
If you need access to App Center, please ask a maintainer to add you.

[wpmobilebot]

You can test the changes in WordPress from this Pull Request by:

• Clicking here or scanning the QR code below
• Then installing the build number pr18320-e72e2fa from App Center on your iPhone

The .ipa file can also be downloaded directly here.
If you need access to App Center, please ask a maintainer to add you.

[dvdchr]

LGTM!

[ScoutHarris]

Thanks @dvdchr !