Regression in `ptr_arg`

Summary

Clippy had displayed ptr_arg warnings before Rust version 1.60

➜  expr git:(master) ✗ cargo +1.59 clippy 
    Checking expr v0.1.0 (/home/maksim/dev/my/expr)
warning: writing `&String` instead of `&str` involves a new object where a slice will do
 --> src/lib.rs:1:15
  |
1 | pub fn foo(_: &String) {}
  |               ^^^^^^^ help: change this to: `&str`
  |
  = note: `#[warn(clippy::ptr_arg)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg

warning: writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used with non-Vec-based slices
 --> src/lib.rs:2:15
  |
2 | pub fn bar(_: &Vec<u8>) {}
  |               ^^^^^^^^ help: change this to: `&[u8]`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg

warning: `expr` (lib) generated 2 warnings
    Finished dev [unoptimized + debuginfo] target(s) in 0.14s
➜  expr git:(master) ✗ cargo +1.60 clippy 
    Checking expr v0.1.0 (/home/maksim/dev/my/expr)
    Finished dev [unoptimized + debuginfo] target(s) in 0.14s

Reproducer

I tried this code:

fn foo(_: &String) {}
fn bar(_: &Vec<u8>) {}

I expected to see this happen:

warning: writing `&String` instead of `&str` involves a new object where a slice will do
 --> src/lib.rs:1:15
  |
1 | pub fn foo(_: &String) {}
  |               ^^^^^^^ help: change this to: `&str`
  |
  = note: `#[warn(clippy::ptr_arg)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg

warning: writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used with non-Vec-based slices
 --> src/lib.rs:2:15
  |
2 | pub fn bar(_: &Vec<u8>) {}
  |               ^^^^^^^^ help: change this to: `&[u8]`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg

Instead, this happened:

No warning

Version

Working:
rustc 1.59.0 (9d1b2106e 2022-02-23)
binary: rustc
commit-hash: 9d1b2106e23b1abd32fce1f17267604a5102f57a
commit-date: 2022-02-23
host: x86_64-unknown-linux-gnu
release: 1.59.0
LLVM version: 13.0.0

Not working:
rustc 1.60.0 (7737e0b5c 2022-04-04)
binary: rustc
commit-hash: 7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c
commit-date: 2022-04-04
host: x86_64-unknown-linux-gnu
release: 1.60.0
LLVM version: 14.0.0

Additional Labels

No response

Start with the src/lib.rs reproducer and compare cargo +1.59 clippy with cargo +1.60 clippy, then trace the ptr_arg lint entry point. Add regression coverage for both &String and &Vec, and verify that the expected warnings return without breaking the existing lint tests.