fix encoding US-ASCII error

[ylwu-amzn]

Description

[Describe what this change achieves]

Issues Resolved

#1111

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[ylwu-amzn]

31 tests completed, 5 failed, 9 skipped
Tests with failures:
 - org.opensearch.ml.rest.RestMLRemoteInferenceIT.testCohereClassifyModel
 - org.opensearch.ml.rest.RestMLRemoteInferenceIT.testCohereGenerateTextModel
 - org.opensearch.ml.rest.RestMLRemoteInferenceIT.testPredictRemoteModel
 - org.opensearch.ml.rest.RestMLRemoteInferenceIT.testOpenAIModerationsModel
 - org.opensearch.ml.rest.RestMLRemoteInferenceIT.testOpenAIEditsModel

[peterzhuamazon]

It is better after the #1114 but still shows this: @ylwu-amzn @ryanbogan

31 tests completed, 3 failed, 9 skipped
Tests with failures:
 - org.opensearch.ml.rest.RestMLRemoteInferenceIT.testPredictRemoteModel
 - org.opensearch.ml.rest.RestMLRemoteInferenceIT.testOpenAIEditsModel
 - org.opensearch.ml.rest.RestMLRemoteInferenceIT.testOpenAIModerationsModel