fix: trans error rollback

[a631807682]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

close #6826

User Case Description

[jinzhu]

If a commit fails, is a rollback needed? Does it automatically rollback?

[iTanken]

If a commit fails, is a rollback needed? Does it automatically rollback?

gorm/finisher_api.go

Lines 638 to 655 in e4e23d2

	} else {
	tx := db.Begin(opts...)
	if tx.Error != nil {
	return tx.Error
	}
	defer func() {
	// Make sure to rollback when panic, Block error or Commit error
	if panicked || err != nil {
	tx.Rollback()
	}
	}()
	if err = fc(tx); err == nil {
	panicked = false
	return tx.Commit().Error
	}
	}

// Make sure to rollback when panic, Block error or Commit error

[jinzhu]

// Make sure to rollback when panic, Block error or Commit error

We code for reality, not for comments ;)

After doing some research, I think that modern databases no longer require calling rollback after a failed commit. We might need to revise the comment above.

[a631807682]

Commit are usually divided into writing commit packet and reading results. If writing fails, we not need to rollback. Failure of reading results usually comes from network errors, which means our rollback may not succeed.
This does not seem to be necessary, is there any actual case?