Auto merge of #103683 - fee1-dead-contrib:fix-deferred-cast-checks-constness, r=oli-obk

Retain ParamEnv constness when running deferred cast checks

Fixes #103677.

src/test/ui/rfc-2632-const-trait-impl/issue-103677.rs

@@ -0,0 +1,5 @@
+// check-pass
+
+const _: fn(&String) = |s| { &*s as &str; };
+
+fn main() {}