fix(mysql): correct error message for x-statement-timeout parsing

[zigzagdev]

Summary

Fix incorrect error message for x-statement-timeout parsing.

Problem

strconv.Atoi is used to parse x-statement-timeout, but the error message incorrectly referred to the value as float.

// Before
return nil, fmt.Errorf("could not parse x-statement-timeout as float: %w", err)

Fix

// After
return nil, fmt.Errorf("could not parse x-statement-timeout as integer: %w", err)

Notes

• Logic is unchanged
• No tests required as this is a string-only fix

[coveralls]

coverage: 54.432%. remained the same
when pulling 793308f on zigzagdev:fix/err-msg-type
into 2bd822b on golang-migrate:master.