Fix conv function behavior discrepancy between Windows and Linux in mysqltest (expr.conv)

[chyujing]

Environment

• Version: Not specified (not a temporary RD-provided version).
• Platforms: Windows, Linux.
• Reproducibility: Stable reproduction.
• Deployment Info: Not specified.
• Logs: Not provided.

Description

The conv function exhibits different behavior when running the expr.conv test case (mysqltest) on Windows versus Linux. The test returns an empty result on Windows, while it produces the expected result on Linux.

Steps to Reproduce

1. Connect to the database using the provided connection string: mysql -uroot -h -P 2881.
2. Execute the expr.conv test case.

Observed Result (Windows): Empty result.
Expected Result (Linux): Correct, non-empty result.

Impact

This is a cross-platform compatibility issue that affects the correctness and consistency of test results and potentially the conv function's behavior in Windows environments.

Additional Information

• The specific SQL or test file for expr.conv was not attached.
• Connection details for the problematic tenant or the sys tenant were not provided.
• It is not specified if the deployment environment was preserved for investigation.