Ignore incompatible_msrv clippy lint for conditionally compiled code

    warning: current MSRV (Minimum Supported Rust Version) is `1.56.0` but this item is stable since `1.66.0`
       --> src/wrapper.rs:514:36
        |
    514 |             Span::Compiler(s) => s.source_text(),
        |                                    ^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv
        = note: `-W clippy::incompatible-msrv` implied by `-W clippy::all`
        = help: to override `-W clippy::all` add `#[allow(clippy::incompatible_msrv)]`

src/lib.rs

@@ -96,6 +96,7 @@
     clippy::cast_possible_truncation,
     clippy::checked_conversions,
     clippy::doc_markdown,
+    clippy::incompatible_msrv,
     clippy::items_after_statements,
     clippy::iter_without_into_iter,
     clippy::let_underscore_untyped,