Unnecessary indentation for a commented block of code

[scampi]

In PR #2925 an integration test on the packed_simd code base failed with the following:

Diff in /home/yfful/documents/code/rustfmt/packed_simd/src/api/from/from_vector.rs at line 18:
         }
 
         // FIXME: `Into::into` is not inline, but due to
-                                                // the blanket impl in `std`, which is not
-                                                // marked `default`, we cannot override it here with
-                                                // specialization.
-                                                /*
-                                                impl Into<$id> for $source {
-                                                    #[inline]
-                                                    fn into(self) -> $id {
-                                                        unsafe { simd_cast(self) }
-                                                    }
-                                                }
-                                                */
+                                                        // the blanket impl in `std`, which is not
+                                                        // marked `default`, we cannot override it here with
+                                                        // specialization.
+                                                        /*
+                                                        impl Into<$id> for $source {
+                                                            #[inline]
+                                                            fn into(self) -> $id {
+                                                                unsafe { simd_cast(self) }
+                                                            }
+                                                        }
+                                                        */

This can be seen when running cargo fmt --all -- --check against
rust-lang/packed_simd@1a6450d

The commented block should not have the extra indentation, i.e., it would be nicer if it were like below:

         }

         // FIXME: `Into::into` is not inline, but due to
         // the blanket impl in `std`, which is not
         // marked `default`, we cannot override it here with
         // specialization.
         /*
         impl Into<$id> for $source {
             #[inline]
             fn into(self) -> $id {
                 unsafe { simd_cast(self) }
             }
         }
         */

[scampi]

duplicate of #2917