Auto merge of #28201 - servo:rustup, r=jdm

Upgrade to rustc 1.52.0-nightly (a8486b64b 2021-02-24)

components/script/dom/treewalker.rs

@@ -467,7 +467,7 @@ impl<'a> Iterator for &'a TreeWalker {
             // which cannot produce an Err result.
             {
                 unreachable!()
-            },
+            }
         }
     }
 }

components/script/lib.rs

@@ -4,6 +4,7 @@
 
 #![feature(assoc_char_funcs)]
 #![feature(const_fn)]
+#![feature(const_fn_fn_ptr_basics)]
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]
 #![feature(plugin)]