testdata: use for loop with full ForClause to prevent gofmt from reformatting it

Author: fzipp

testdata/loops.go

@@ -22,6 +22,6 @@ func l4() {
 	}
 	for true {
 	}
-	for ;; {
+	for i := 0; i < 10; i++ {
 	}
 }