[ads] Fixes allow brave://settings/search/defaultSearch deep link

[tmancey]

Resolves brave/brave-browser#44745

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

Confirm ads can deep link to chrome://settings/search/defaultSearch

[aseren]

LGTM

[tmancey]

Missed when adding brave/brave-browser#42999, thanks

[github-actions]

Chromium major version is behind target branch (134.0.6998.95 vs 135.0.7049.17). Please rebase.

[brave-builds]

Released in v1.78.56

[btlechowski]

Verified with

Brave	1.78.58 Chromium: 135.0.7049.26 (Official Build) nightly (64-bit)
Revision	e2eeb23
OS	Linux

non rewards

Note: the target url points to chrome://settings/search/defaultSearch

Verified link points brave://settings/search/defaultSearch

Verified clicking the ad opens brave://settings/search/defaultSearch

rewards

Note: the target url points to chrome://settings/search/defaultSearch

Verified link points brave://settings/search/defaultSearch

Verified clicking the ad opens brave://settings/search/defaultSearch