sql/schmachanger: use more friendly language for fallback

Previously, the declarative schema changer used slightly
alarming language when falling back. To address this,
this patch removes the word failure and uses softer
langauge.

Fixes: cockroachdb#97922

Release note: None

pkg/sql/schemachanger/scerrors/errors.go

@@ -75,7 +75,7 @@ func (el EventLogger) HandlePanicAndLogError(ctx context.Context, err *error) {
 			log.InfofDepth(ctx, depth, "done %s in %s", el.msg, redact.Safe(timeutil.Since(el.start)))
 		}
 	case HasNotImplemented(*err):
-		log.InfofDepth(ctx, depth, "failed %s with error: %v", el.msg, *err)
+		log.InfofDepth(ctx, depth, "unsuccessful in %s with message: %v", el.msg, *err)
 	case errors.HasAssertionFailure(*err):
 		*err = errors.Wrapf(*err, "%s", el.msg)
 		fallthrough