Fix instruction text placeholder replacement

[LuXcDD]

Summary

This PR fixes a bug in CarlaVoiceDataset where instruction placeholders were not actually replaced in instruction_text.

The previous code called str.replace(...) without assigning the returned string back to instruction_text. Since Python strings are immutable, placeholders such as [x], left/right, and [y] remained unchanged.

Changes

• Assign the result of instruction_text.replace(...) back to instruction_text
• Preserve the existing placeholder handling logic and exception flow

Why this matters

This ensures generated instruction text correctly reflects values from info['instruction_args'] instead of leaving template placeholders in the final string.

Testing

• Verified the replacement logic now updates instruction_text as intended
• No additional tests were run