Un-customized default search engine should be Naver, not Google, on upgrade

[stephendonner]

Description

Un-customized default search engine should be Naver, not Google, on upgrade

Found while testing #18855

Steps to Reproduce

1. set OS region to South Korea
2. install 1.50.114
3. launch Brave
4. open brave://settings/search
5. confirm and leave search-engine defaults of Google and Brave for Normal window and Private window, respectively
6. installed 1.51.79 atop
7. launched Brave
8. opened brave://settings/search

Actual result:

Google remains the default for Normal window, and Brave is (correctly) default for Private window

1.50.114	1.51.79

Expected result:

Naver (in Unicode) should be default for Normal window, if the user hasn't customized their default from 1.50.114

Reproduces how often:

100%

Brave version (brave://version info)

Brave	1.51.78 Chromium: 112.0.5615.49 (공식 빌드) beta (x86_64)
개정	bd2a7bcb881c11e8cfe3078709382934e3916914-refs/branch-heads/5615@{#936}
OS	macOS 버전 11.7.5(빌드 20G1225)

Version/Channel Information:

• Can you reproduce this issue with the current release?
• Can you reproduce this issue with the beta channel?
• Can you reproduce this issue with the nightly channel?

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Miscellaneous Information:

/cc @simonhong @rebron @brave/qa-team