Add some regression tests

Author: camelid

src/test/ui/issues/issue-75763.rs

@@ -0,0 +1,14 @@
+// build-pass
+
+#![allow(incomplete_features)]
+#![feature(const_generics)]
+
+struct Bug<const S: &'static str>;
+
+fn main() {
+    let b: Bug::<{
+        unsafe {
+            std::mem::transmute::<&[u8], &str>(&[0xC0, 0xC1, 0xF5])
+        }
+    }>;
+}

src/test/ui/issues/issue-76179.rs

@@ -0,0 +1,19 @@
+// check-pass
+
+#![feature(associated_type_defaults)]
+
+use std::io::Read;
+
+trait View {
+    type Deserializers: Deserializer<Item = Self::RequestParams>;
+    type RequestParams = DefaultRequestParams;
+}
+
+struct DefaultRequestParams;
+
+trait Deserializer {
+    type Item;
+    fn deserialize(r: impl Read) -> Self::Item;
+}
+
+fn main() {}