fix: suppress false positive unused_assignments warnings in Rust 1.92

Add #![allow(unused_assignments)] at crate level to suppress false positive
warnings introduced by Rust 1.92's stricter lint behavior on code generated
by the enum-as-inner derive macro.

This is a known Rust compiler bug tracked at:
- rust-lang/rust#147648

The fix for enum-as-inner is pending at:
- bluejekyll/enum-as-inner#108

The allow can be removed once enum-as-inner is updated.

Co-Authored-By: Maximilian Roos <max-sixty@users.noreply.github.com>

Author: github-actions[bot]

prqlc/prqlc/src/lib.rs

@@ -35,6 +35,11 @@
 //! ```
 //!
 #![doc = include_str!("../ARCHITECTURE.md")]
+// TODO: remove when enum-as-inner is updated with the fix from
+// https://github.com/bluejekyll/enum-as-inner/pull/108
+// This suppresses false positive warnings from Rust 1.92+:
+// https://github.com/rust-lang/rust/issues/147648
+#![allow(unused_assignments)]
 //!
 //! ## Common use-cases
 //!