Blogging Prompts: Update prompt card lightbulb icon

[dvdchr]

Refs #18250
Depends on #18320

As titled, this updates the lightbulb icon from SFSymbols to icon-lightbulb-outline.

Before	After

To test

• Turn on Blogging Prompts and My Site Dashboard feature flags.
• Go to My Site Dashboard, Home tab.
• Verify that the prompt card is displayed with the new lightbulb icon.

Regression Notes

1. Potential unintended areas of impact
   N/A. Feature is under development.

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

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

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 WordPress from this Pull Request by:

• Clicking here or scanning the QR code below
• Then installing the build number pr18333-3e45526 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 Jetpack from this Pull Request by:

• Clicking here or scanning the QR code below
• Then installing the build number pr18333-3e45526 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.

[ScoutHarris]

💡 🪄 .