Fixes https://github.com/mattermost/mattermost/issues/29102
- Fix error handling in fileutils.FindDir() call by properly checking the returned boolean value
- Add proper error handling for SetPhase2PermissionsMigrationStatus calls
- Remove channels/app/support_packet_test.go from the errcheck exception list in .golangci.yml
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Co-authored-by: Claude <noreply@anthropic.com>