Ignore return_self_not_must_use clippy lint

    error: missing `#[must_use]` attribute on a method returning `Self`
       --> src/error.rs:296:5
        |
    296 | /     pub fn context<C>(self, context: C) -> Self
    297 | |     where
    298 | |         C: Display + Send + Sync + 'static,
    299 | |     {
    ...   |
    323 | |         unsafe { Error::construct(error, vtable, backtrace) }
    324 | |     }
        | |_____^
        |
        = note: `-D clippy::return-self-not-must-use` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#return_self_not_must_use

src/lib.rs

@@ -225,6 +225,7 @@
     clippy::needless_doctest_main,
     clippy::new_ret_no_self,
     clippy::redundant_else,
+    clippy::return_self_not_must_use,
     clippy::unused_self,
     clippy::used_underscore_binding,
     clippy::wildcard_imports,