Fix conversion bug when string data comes from binlog

[mattbooks]

Related issue: #1568

Description

This PR fixes a string conversion bug by applying character set conversions when the input is []uint8, in addition to the existing case of when the input is string.

When using gh-ost to migrate a table from latin1 to utf8mb3 character encoding, the initial data copy works correctly, but new data with special characters inserted during the migration via binlog replication fails with "Incorrect string value" errors.

The reason for this is that the data is a binary byte array when converted from the binlog, so the character set conversion is not applied.

I added a new test for latin1-encoded byte array input to this method and confirmed that the reproduction from the linked issue is fixed with this change.

• contributed code is using same conventions as original code
• script/cibuild returns with no formatting errors, build errors or unit test errors.

[Copilot]

Pull Request Overview

This PR fixes a character set conversion bug in gh-ost when handling string data from binlog replication. The issue occurs when migrating tables from latin1 to utf8mb3 encoding, where special characters in binlog data fail with "Incorrect string value" errors because the data comes as a byte array ([]uint8) rather than a string, bypassing the existing character set conversion logic.

• Extends the convertArg method to handle []uint8 input in addition to existing string input
• Updates character set conversion to use Bytes() method instead of String() for more consistent handling
• Adds comprehensive test coverage for latin1-encoded byte array conversion

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
go/sql/types.go	Modified convertArg method to handle []uint8 input and use byte-based charset conversion
go/sql/types_test.go	Added test case for latin1 byte array character set conversion

Comments suppressed due to low confidence (1)

go/sql/types.go:56

• [nitpick] The variable name 'arg2Bytes' is unclear and could be confusing. Consider renaming it to 'argBytes' or 'inputBytes' to better reflect its purpose as the byte representation of the input argument.

	var arg2Bytes []byte