Remove subdirectories from mappings for sbt 2

[BillyAutrey]

In sbt 2.0, mappings has changed type to a Seq[HashedVirtualFileRef]. If any directories are in mappings, calls to package will fail with an error like this:

[info] [error] (e / Compile / packageBin) java.io.IOException: Is a directory

sbt 2 will either have to accomodate subdirectories in mappings, or else this library will have to filter them out of mappings.

[BillyAutrey]

This is blocking #255.

[BillyAutrey]

This is a naive approach, but it experimentally got package to succeed.

===================================================================
diff --git a/src/main/scala/com/typesafe/sbt/web/SbtWeb.scala b/src/main/scala/com/typesafe/sbt/web/SbtWeb.scala
--- a/src/main/scala/com/typesafe/sbt/web/SbtWeb.scala	(revision 99b81eb4d07635e68fb41c04237a712603004faa)
+++ b/src/main/scala/com/typesafe/sbt/web/SbtWeb.scala	(date 1729716374650)
@@ -549,7 +560,9 @@
   ): Seq[PathMapping] = {
     implicit val fc: FileConverter = conv
     if (deduplicators.isEmpty) {
-      mappings
+      mappings.filter { case (fileRef, string) =>
+        !toFile(fileRef).isDirectory
+      }
     } else {
       mappings.groupBy(_._2 /*path*/ ).toSeq flatMap { grouped =>
         val (path, group) = grouped