fix undefined SETTING_ENABLE_DEBUG_MODE

[rawdreeg]

Changes proposed in this Pull Request:

This is something that escaped our attention in this PR: #2754. The constant SETTING_ENABLE_DEBUG_MODE should not be called from self. but from WC_Facebookcommerce_Integration.

Closes #2778.

• Do the changed files pass phpcs checks? Please remove phpcs:ignore comments in changed files and fix any issues, or delete if not practical.

Screenshots:

Detailed test instructions:

Upgrade the plugin from version 1, and no errors should occur.

Changelog entry

Fix - Update failing due to undefined constant error in Lifecycle

[lynnjat7]

Just noting that the original reporting customer on this tried the code fix already (@rawdreeg provided it to me on Slack) and it worked, so looks like clear sailing for this fix.
8503847-zen

[rawdreeg]

I'll merge this one without a review

[ecgan]

Closes #2278.

@rawdreeg , I believe you have a typo above. I have edited your PR description to "Closes #2778."

[rawdreeg]

Thanks, @ecgan

[layoutd]

Thanks for identifying and cleaning this up, @rawdreeg