privacy: Fix regression in impl reachability

src/test/ui/privacy/auxiliary/issue-57264.rs

@@ -0,0 +1,9 @@
+mod inner {
+    pub struct PubUnnameable;
+}
+
+pub struct Pub<T>(T);
+
+impl Pub<inner::PubUnnameable> {
+    pub fn pub_method() {}
+}

src/test/ui/privacy/issue-57264.rs

@@ -0,0 +1,8 @@
+// compile-pass
+// aux-build:issue-57264.rs
+
+extern crate issue_57264;
+
+fn main() {
+    issue_57264::Pub::pub_method();
+}