chore(query): refine set sql_dialect error message

[Dousir9]

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Summary

Refine set sql_dialect error message: set sql_dialect = experimental -> set sql_dialect = 'experimental'.

• Related to unnest bug: Unable to get field named "18446744073709551615". Valid fields: ["0"] #13800

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Change error message, no need test.

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe): change error message

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This change is