Update to nightly-2026-07-15

[Wassasin]

Update the Rust toolchain version to nightly-2026-07-15.

Changes in the test-suite can be attributed to core/std changes and compilation optimization changes in rustc. These are to be expected. Important is that the so-called lint boundary is identical, which is the case here.

Secondly the special consideration for shims in get_call_def_mir has been removed as it relates to std::ops::Fn::call as part of the fn_traits unstable feature. We are already emitting a lint if the function is cast to a pointer, so this part was redundant. It has been removed because due to the update of the toolchain fn_args now has a Binder and needed to be updated.