Strange inferred Any error on +: in Scala 2.13

[steinybot]

I am getting the following errors on https://github.com/BotTech/scala2plantuml/blob/e511e8ac6bb3ec1cc57d31917d52722acc41074c/core/src/main/scala/nz/co/bottech/scala2plantuml/ClassDiagramRenderer.scala#L130:

sbt:scala2plantuml> compile
[info] compiling 15 Scala sources to /Users/jason/source/scala2plantuml/core/target/scala-2.13/classes ...
[error] /Users/jason/source/scala2plantuml/core/src/main/scala/nz/co/bottech/scala2plantuml/ClassDiagramRenderer.scala:115:19: [wartremover:Any] Inferred type containing Any: [_]Seq[_]
[error]         case head +: tail =>
[error]                   ^
[error] /Users/jason/source/scala2plantuml/core/src/main/scala/nz/co/bottech/scala2plantuml/DiagramModifications.scala:75:43: [wartremover:Any] Inferred type containing Any: [_]Seq[_]
[error]           case (aggregation: Aggregation) +: tail if aggregations.contains(aggregation) =>
[error]                                           ^
[error] /Users/jason/source/scala2plantuml/core/src/main/scala/nz/co/bottech/scala2plantuml/DiagramModifications.scala:77:43: [wartremover:Any] Inferred type containing Any: [_]Seq[_]
[error]           case (aggregation: Aggregation) +: tail =>
[error]                                           ^
[error] /Users/jason/source/scala2plantuml/core/src/main/scala/nz/co/bottech/scala2plantuml/DiagramModifications.scala:79:21: [wartremover:Any] Inferred type containing Any: [_]Seq[_]
[error]           case head +: tail =>
[error]                     ^
[error] /Users/jason/source/scala2plantuml/core/src/main/scala/nz/co/bottech/scala2plantuml/DiagramModifications.scala:100:32: [wartremover:Any] Inferred type containing Any: [_]Seq[_]
[error]               case (typ: Type) +: tail =>
[error]                                ^
[error] /Users/jason/source/scala2plantuml/core/src/main/scala/nz/co/bottech/scala2plantuml/DiagramModifications.scala:103:37: [wartremover:Any] Inferred type containing Any: [_]Seq[_]
[error]               case (member: Member) +: tail =>
[error]                                     ^
[error] /Users/jason/source/scala2plantuml/core/src/main/scala/nz/co/bottech/scala2plantuml/DiagramModifications.scala:119:25: [wartremover:Any] Inferred type containing Any: [_]Seq[_]
[error]               case head +: tail =>
[error]                         ^
[error] /Users/jason/source/scala2plantuml/core/src/main/scala/nz/co/bottech/scala2plantuml/SemanticdbLoader.scala:23:19: [wartremover:Any] Inferred type containing Any: [_]Seq[_]
[error]         case head +: tail =>
[error]                   ^

It only happens when cross building for Scala 2.13.4 (sbt ++2.13.4 compile).

Apologies that I haven't had a chance to minimize this.