Fixes Brave Ads Purchase Intent segments should fall back to parent segments - 1.14.x

[tmancey]

Uplift of #6483
Resolves brave/brave-browser#11410

• You have checked CI and the builds, lint, and tests all pass or are not related to your PR.
• You have tested your change on Nightly.
• The PR milestones match the branch they are landing to.

After you merge:

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[kjozwiak]

Restarting both Android & Win x64 as both timed out and never finished.

[kjozwiak]

test-browser failed on Win x64 due to GreaselionServiceTest.ScriptInjectionWithPrecondition failing as per https://ci.brave.com/job/pr-brave-browser-issues-11410-1.14.x-windows/2/execution/node/216/log/. However, this a known intermittent issue and doesn't block uplift.

18:48:41  [  FAILED  ] GreaselionServiceTest.ScriptInjectionWithPrecondition, where TypeParam =  and GetParam() =  (2812 ms)
18:48:41  
18:48:41  [606/606] GreaselionServiceTest.ScriptInjectionWithPrecondition (2986 ms)

18:48:41  1 test failed:
18:48:41      GreaselionServiceTest.ScriptInjectionWithPrecondition (../../brave/browser/greaselion/greaselion_browsertest.cc:265)

[kjozwiak]

Uplift into 1.14.x approved after deliberating with @brave/uplift-approvers. QA has verified the PR on Nightly as per #6483 (comment).