Ignore buggy ptr_arg clippy lint

rust-lang/rust-clippy#8366

    error: writing `&mut Vec` instead of `&mut [_]` involves a new object where a slice will do
      --> src/read.rs:65:45
       |
    65 |     fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'de, 's, str>>;
       |                                             ^^^^^^^^^^^^^^^ help: change this to: `&'s mut [u8]`
       |
       = note: `-D clippy::ptr-arg` implied by `-D clippy::all`
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg

    error: writing `&mut Vec` instead of `&mut [_]` involves a new object where a slice will do
      --> src/read.rs:76:18
       |
    76 |         scratch: &'s mut Vec<u8>,
       |                  ^^^^^^^^^^^^^^^ help: change this to: `&'s mut [u8]`
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg

Author: dtolnay

src/lib.rs

@@ -314,6 +314,8 @@
     clippy::match_single_binding,
     clippy::needless_doctest_main,
     clippy::needless_late_init,
+    // clippy bug: https://github.com/rust-lang/rust-clippy/issues/8366
+    clippy::ptr_arg,
     clippy::return_self_not_must_use,
     clippy::transmute_ptr_to_ptr,
     clippy::unnecessary_wraps,