Update DEPS to include new brave-extension

[bsclifton]

after brave/brave-extension#67 was merged

That commit adds "incognito": "split" to the extension manifest (matching browser-laptop behavior)

Helps with addressing brave/brave-browser#1198

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone

Test Plan:

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

[bsclifton]

master 78c5c7d
0.56.x 64e0be2
0.55.x 65c323f