yanglint cannot handle single `uses` in `sx:augment-structure`

[micnovak]

Use following YANG datamodel (file example.yang):

module example {
    yang-version 1.1;
    namespace "ex:ample";
    prefix example;

    import ietf-yang-structure-ext {
        prefix sx;
    }

    grouping files {
        container files {
            list file {
                key id;

                leaf id {
                    type uint32;
                }
            }
        }
    }

    sx:structure struct {
        container c {
            leaf b {
                type uint32;
            }
        }
    }

    sx:augment-structure "/example:struct/c" {
        //leaf a {type uint32;}
        uses files;
    }
}

yanglint 3.7.8

yanglint example.yang
libyang err : Ext plugin "ly2 structure v1": Extension sx:augment-structure does not define any data-def-stmt statements. (/example:{extension='sx:augment-structure'}//example:struct/c)

According to https://datatracker.ietf.org/doc/html/rfc7950#section-14 , uses is part of the data-def-stmt (uses-stmt)

   data-def-stmt       = container-stmt /
                         leaf-stmt /
                         leaf-list-stmt /
                         list-stmt /
                         choice-stmt /
                         anydata-stmt /
                         anyxml-stmt /
                         uses-stmt

When you add artificial leaf like below, it works fine.

    sx:augment-structure "/example:struct/c" {
        leaf a {type uint32;}
        uses files;
    }

[michalvasko]

Fixed.