Ignore buggy clippy::lint_groups_priority lint

rust-lang/rust-clippy#12270

```
error: lint group `rust_2018_idioms` has the same priority (0) as a lint
  --> Cargo.toml:50:1
   |
50 | rust_2018_idioms = "warn"
   | ^^^^^^^^^^^^^^^^   ------ has an implicit priority of 0
51 | single_use_lifetimes = "warn"
   | -------------------- has the same priority as this lint
   |
   = note: the order of the lints in the table is ignored by Cargo
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#lint_groups_priority
   = note: `-D clippy::lint-groups-priority` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::lint_groups_priority)]`
help: to have lints override the group set `rust_2018_idioms` to a lower priority
   |
50 | rust_2018_idioms = { level = "warn", priority = -1 }
   |                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

error: lint group `all` has the same priority (0) as a lint
  --> Cargo.toml:55:1
   |
55 | all = "warn" # Downgrade deny-by-default lints
   | ^^^   ------ has an implicit priority of 0
56 | pedantic = "warn"
57 | as_ptr_cast_mut = "warn"
   | --------------- has the same priority as this lint
   |
   = note: the order of the lints in the table is ignored by Cargo
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#lint_groups_priority
help: to have lints override the group set `all` to a lower priority
   |
55 | all = { level = "warn", priority = -1 } # Downgrade deny-by-default lints
   |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

error: lint group `pedantic` has the same priority (0) as a lint
  --> Cargo.toml:56:1
   |
56 | pedantic = "warn"
   | ^^^^^^^^   ------ has an implicit priority of 0
57 | as_ptr_cast_mut = "warn"
   | --------------- has the same priority as this lint
   |
   = note: the order of the lints in the table is ignored by Cargo
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#lint_groups_priority
help: to have lints override the group set `pedantic` to a lower priority
   |
56 | pedantic = { level = "warn", priority = -1 }
   |            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

Cargo.toml

@@ -66,6 +66,7 @@ borrow_as_ptr = { level = "allow", priority = 1 } # https://github.com/rust-lang
 declare_interior_mutable_const = { level = "allow", priority = 1 } # https://github.com/rust-lang/rust-clippy/issues/7665
 doc_markdown = { level = "allow", priority = 1 }
 float_cmp = { level = "allow", priority = 1 } # https://github.com/rust-lang/rust-clippy/issues/7725
+lint_groups_priority = { level = "allow", priority = 1 } # https://github.com/rust-lang/rust-clippy/issues/12270
 manual_assert = { level = "allow", priority = 1 }
 manual_range_contains = { level = "allow", priority = 1 } # https://github.com/rust-lang/rust-clippy/issues/6455#issuecomment-1225966395
 missing_errors_doc = { level = "allow", priority = 1 }