knotserver: log workflow parsing errors

Signed-off-by: Anirudh Oppiliappan <[e-mail]>

knotserver/internal.go

···
 		wf, err := workflow.FromFile(e.Name, contents)
 		if err != nil {
 			// TODO: log here, respond to client that is pushing
+			h.l.Error("failed to parse workflow", "err", err, "path", fpath)
 			continue
 		}