v3.6 $setOnInsert may create objects with dots in field names

v3.4 used to fail in this case because dots are not allowed in field names.
I did not find anything related in release notes, so it looks like a potential regression.

The following command adds a document which sub-document has a field "bad.1"

{{> db.test.update({y : {y :

{"bad.1" : 1}

} }, {$setOnInsert :

{x : 42}

},

{upsert : true}

)
WriteResult(

{ "nMatched" : 0, "nUpserted" : 1, "nModified" : 0, "_id" : ObjectId("5a2d066a88785e4c179faaa1") }

)

> db.test.find()
{ "_id" : ObjectId("5a2d066a88785e4c179faaa1"), "y" : { "y" :

{ "bad.1" : 1 }

}, "x" : 42 }
}}