Update dark mode color

[kean]

I cherry-picked the change from #23587, but only for Jetpack for now. I've been testing the dark mode version extensively on my personal devices, and the current green does appear too dark and it not legible. You typically want to use colors that are slightly lighter in dark mode, so this PR does that.

The color in light mode is unchanged.

To test:

Regression Notes

1. Potential unintended areas of impact

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

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

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.

Testing checklist:

• WordPress.com sites and self-hosted Jetpack sites.
• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• VoiceOver.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• iPhone and iPad.
• Multi-tasking: Split view and Slide over. (iPad)

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 25.4. This milestone is due in less than 4 days. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

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[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Alpha by scanning the QR code below to install the corresponding build.

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr23619-4d165c7
	Version	25.3
	Bundle ID	org.wordpress.alpha
	Commit	4d165c7
	App Center Build	WPiOS - One-Offs #10717

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Alpha by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr23619-4d165c7
	Version	25.3
	Bundle ID	com.jetpack.alpha
	Commit	4d165c7
	App Center Build	jetpack-installable-builds #9760

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.