add regression test for cached lint expectations

Author: Bryntet

tests/incremental/cache-lint-expectation.rs

@@ -0,0 +1,8 @@
+// Regression test for #154878
+//@ revisions: cpass1 cpass2
+
+pub fn main() {
+    let x = 42.0;
+    #[expect(invalid_nan_comparisons)]
+    let _b = x == f32::NAN;
+}