Duplicate error for using allow inside forbid

Code

// USE `-Zdeduplicate-diagnostics=false`
#[forbid(unsafe_code)] // NO UNSAFE CODE IN HERE!!
fn main() {
    {
        #[allow(unsafe_code)] // let's have some unsafe code in here
        {
        }
    }
}

Current output

error[E0453]: allow(unsafe_code) incompatible with previous forbid
 --> tests/ui/lint/deny-inside-forbid-ignored.rs:4:17
  |
1 | #[forbid(unsafe_code)] // NO UNSAFE CODE IN HERE!!
  |          ----------- `forbid` level set here
...
4 |         #[allow(unsafe_code)] // let's have some unsafe code in here
  |                 ^^^^^^^^^^^ overruled by previous forbid

error[E0453]: allow(unsafe_code) incompatible with previous forbid
 --> tests/ui/lint/deny-inside-forbid-ignored.rs:4:17
  |
1 | #[forbid(unsafe_code)] // NO UNSAFE CODE IN HERE!!
  |          ----------- `forbid` level set here
...
4 |         #[allow(unsafe_code)] // let's have some unsafe code in here
  |                 ^^^^^^^^^^^ overruled by previous forbid
  |
  = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0453`.

Desired output

error[E0453]: allow(unsafe_code) incompatible with previous forbid
 --> tests/ui/lint/deny-inside-forbid-ignored.rs:4:17
  |
1 | #[forbid(unsafe_code)] // NO UNSAFE CODE IN HERE!!
  |          ----------- `forbid` level set here
...
4 |         #[allow(unsafe_code)] // let's have some unsafe code in here
  |                 ^^^^^^^^^^^ overruled by previous forbid

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0453`.

Rationale and extra context

Use -Zdeduplicate-diagnostics=false

more context can be found in tests/ui/lint/issue-70819-dont-override-forbid-in-same-scope.rs

Other cases

No response

Rust Version

rustc 1.83.0-nightly (14f303bc1 2024-10-04)
binary: rustc
commit-hash: 14f303bc1430a78ddaa91b3e104bbe4c0413184e
commit-date: 2024-10-04
host: x86_64-unknown-linux-gnu
release: 1.83.0-nightly
LLVM version: 19.1.0

Anything else?

No response

Start with tests/ui/lint/deny-inside-forbid-ignored.rs and reproduce the output using -Zdeduplicate-diagnostics=false; then read tests/ui/lint/issue-70819-dont-override-forbid-in-same-scope.rs for related behavior. Done means the allow-inside-forbid case emits one E0453 diagnostic and reports one previous error.