fix(scoop-search): Require files in 'bucket' dir for remote known buckets

[amorphobia]

Change regex in function search_remote: only matches json files inside 'bucket' directory.

Description

All known buckets store manifest json files in 'bucket' directory. Current scoop-search.ps1 use a regex that may match json files in the root directory, which is unnecessary for them. This small change let the 'bucket' directory be required.

Motivation and Context

Closes #4943

How Has This Been Tested?

1. Run regression and all tests passed:

Tests completed in 38.78s
Tests Passed: 125, Failed: 0, Skipped: 0, Pending: 0, Inconclusive: 0

2. Try the command in issue [Bug] scoop search for remote buckets might get irrelevant json files #4943 and got output as expected:

scoop.ps1 search markdownlint
No matches found.

3. Run with an exist app to make sure it's not broken:

scoop.ps1 search minecraft
Results from other known buckets...
(add them using 'scoop bucket add <name>')

'games' bucket (install using 'scoop install games/<app>'):
    minecraft

Checklist:

• I have read the Contributing Guide.
• I have ensured that I am targeting the develop branch.
• I have updated the documentation accordingly.
• I have updated the tests accordingly.
• I have added an entry in the CHANGELOG.

[niheaven]

Though this is merged, the changelog entry has error... Please use PR number, not issue number, in changelog.