🐛 fix incorrect rendering of non-closing tags (eg. <br></br>) (#8749)
🐛 fix incorrect rendering of non-closing tags (eg. <br></br>) (#8749)

closes https://github.com/TryGhost/Ghost/issues/8743

- the serializer in our mobiledoc renderer didn't have the list of non-closing HTML tags passed in which meant that tags such as `<br>` in the markdown HTML output were being re-serialized to `<br></br>` which is invalid HTML which (at least Chrome) then attempts to fix by rendering it as `<br><br>` instead
- the elements with incorrect rendering that may result in unwanted "fixing" by browsers are `AREA`, `BASE`, `BR`, `COL`, `COMMAND`, `EMBED`, `HR`, `IMG`, `INPUT`, `KEYGEN`, `LINK`, `META`, `PARAM`, `SOURCE`, `TRACK`, and `WBR`
JohnONolan/Ghost,mohanambati/Ghost,ErisDS/Ghost,cwonrails/Ghost,BlueHatbRit/Ghost,cwonrails/Ghost,BlueHatbRit/Ghost,leninhasda/Ghost,leninhasda/Ghost,kevinansfield/Ghost,e10/Ghost,Gargol/Ghost,mohanambati/Ghost,acburdine/Ghost,sebgie/Ghost,Gargol/Ghost,acburdine/Ghost,cwonrails/Ghost,mohanambati/Ghost,Kikobeats/Ghost,Kikobeats/Ghost,dbalders/Ghost,acburdine/Ghost,dbalders/Ghost,dbalders/Ghost,bitjson/Ghost,sebgie/Ghost,janvt/Ghost,bitjson/Ghost,TryGhost/Ghost,e10/Ghost,ErisDS/Ghost,JohnONolan/Ghost,ErisDS/Ghost,chevex/undoctrinate,TryGhost/Ghost,TryGhost/Ghost,JohnONolan/Ghost,janvt/Ghost,kevinansfield/Ghost,Kikobeats/Ghost,sebgie/Ghost,kevinansfield/Ghost