Parse integer suffix beginning with a hex digit

[dtolnay]

Previously e.g. 0o0A would fail to lex because A is not a permissible octal digit. It doesn't need to be a digit though. This is an octal literal 0o0 with suffix A.

This matches libproc_macro's behavior which parses it as:

Literal {
    kind: Integer,
    symbol: "0o0",
    suffix: Some("A"),
    span: #7 bytes(88..92),
}

dtolnay/syn#897