Auto merge of #6818 - dtolnay:comma, r=alexcrichton

Auto merge of #6818 - dtolnay:comma, r=alexcrichton

Accept trailing comma in test of impl Debug for PackageId

The standard library is planning to begin emitting trailing commas in multiline Debug representations to align with the dominant style in modern Rust code -- https://github.com/rust-lang/rust/pull/59076.

```diff
  PackageId {
      name: "foo",
      version: "1.0.0",
-     source: "registry `https://github.com/rust-lang/crates.io-index`"
+     source: "registry `https://github.com/rust-lang/crates.io-index`",
  }
```

For now, change this tests to accept both with and without trailing comma. Once the trailing comma change reaches the stable channel we will be able to remove one of the cases.