Ignore buggy nonstandard_macro_braces clippy lint

Clippy bug: rust-lang/rust-clippy#7422

    error: use of irregular braces for `write!` macro
     --> tests/test_boxed.rs:6:10
      |
    6 | #[derive(Error, Debug)]
      |          ^^^^^
      |
      = note: `-D clippy::nonstandard-macro-braces` implied by `-D clippy::all`
    help: consider writing `Error`
     --> tests/test_boxed.rs:6:10
      |
    6 | #[derive(Error, Debug)]
      |          ^^^^^
      = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#nonstandard_macro_braces
      = note: this error originates in the derive macro `Error` (in Nightly builds, run with -Z macro-backtrace for more info)

    error: use of irregular braces for `write!` macro
      --> tests/test_context.rs:36:10
       |
    36 | #[derive(Error, Debug)]
       |          ^^^^^
       |
       = note: `-D clippy::nonstandard-macro-braces` implied by `-D clippy::all`
    help: consider writing `Error`
      --> tests/test_context.rs:36:10
       |
    36 | #[derive(Error, Debug)]
       |          ^^^^^
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#nonstandard_macro_braces
       = note: this error originates in the derive macro `Error` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/test_boxed.rs

@@ -1,3 +1,8 @@
+#![allow(
+    // Clippy bug: https://github.com/rust-lang/rust-clippy/issues/7422
+    clippy::nonstandard_macro_braces,
+)]
+
 use anyhow::anyhow;
 use std::error::Error as StdError;
 use std::io;

tests/test_context.rs

@@ -1,3 +1,8 @@
+#![allow(
+    // Clippy bug: https://github.com/rust-lang/rust-clippy/issues/7422
+    clippy::nonstandard_macro_braces,
+)]
+
 mod drop;
 
 use crate::drop::{DetectDrop, Flag};