fix: s3 connector test failures in main-cron

[Rossil2012]

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What's changed and what's your intention?

Build: https://buildkite.com/risingwavelabs/main-cron/builds/1398

Cause: FORMAT PLAIN ENCODE JSON is built into a PlainParser by #13707, which prevents json files to be split by lines within nd_streaming. And simd_json::to_borrowed_value throws an error when parsing the string of multiple json objects (e.g. "{a: 1} {b: 2}") .

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[Rossil2012]

Close as fixed in #14222.