Fix wrong check for site plan sync

[itsmeichigo]

Following up with an internal discussion: p1686154005250689/1686153929.996589-slack-C03L1NF1EA3

Description

@joshheald found that I made a mistake in the check for plan site sync as the logic check for skipping the site plan sync should check for WPCom login instead of the other way around. This error was from #8638 when I switch the logic from using siteID to using isAuthenticatedWithoutWPCom.

Testing instructions

It's not straightforward to test DefaultStoresManager for this fix, and the site sync doesn't work properly after creating a free trial site so it's tricky to test this issue. I'd suggest putting a breakpoint inside the if block to make sure that it's triggered only for when you log in with WPCom.

Screenshots

N/A

---

• 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 from this Pull Request by:

• Clicking here or scanning the QR code below to access App Center
• Then installing the build number pr9900-fcf223f on your iPhone

If you need access to App Center, please ask a maintainer to add you.

[selanthiraiyan]

I validated that the if block is called only when logging in using WPCOM creds. It doesn't fire when logging in using wp-admin creds.

🚀