fix: skip publish on synthetic aggregate root

**Problem**
There's been previous attempt like 1878 to skip publishing of the root,
but it seems like the behavior has regressed at some point in time.

**Solution**
This skips publishing on synthetic aggregate root project.

main/src/main/scala/sbt/internal/BuildDef.scala

@@ -10,12 +10,13 @@ package sbt
 package internal
 
 import java.io.File
-import Keys.{ organization, thisProject, autoGeneratedProject }
+import Keys.{ organization, thisProject, autoGeneratedProject, publish, publishLocal, skip }
 import Def.Setting
 // import sbt.ProjectExtra.apply
 import sbt.io.Hash
 import sbt.internal.util.{ Attributed, StringAttributeMap }
 import sbt.internal.inc.{ FileAnalysisStore, ReflectUtilities }
+import sbt.SlashSyntax0.*
 import xsbti.{ FileConverter, VirtualFileRef }
 import xsbti.compile.CompileAnalysis
 
@@ -42,7 +43,7 @@ private[sbt] object BuildDef:
   }
 
   def defaultAggregated(id: String, aggregate: Seq[ProjectRef]): BuildDef = new BuildDef {
-    override def projectDefinitions(base: File) =
+    override def projectDefinitions(base: File): Seq[Project] =
       defaultAggregatedProject(id, base, aggregate) :: Nil
   }
 
@@ -55,12 +56,18 @@ private[sbt] object BuildDef:
   def defaultAggregatedProject(id: String, base: File, agg: Seq[ProjectRef]): Project =
     defaultProject(id, base).aggregate(agg: _*)
 
-  private[sbt] def generatedRootWithoutIvyPlugin(
+  private[sbt] def generatedRootSkipPublish(
       id: String,
       base: File,
       agg: Seq[ProjectRef]
   ): Project =
-    Project.mkGeneratedRoot(id, base, agg).settings(defaultProjectSettings)
+    Project
+      .mkGeneratedRoot(id, base, agg)
+      .settings(
+        defaultProjectSettings,
+        publish / skip := true,
+        publishLocal / skip := true,
+      )
 
   private[sbt] def defaultProjectSettings: Seq[Setting[_]] = Seq(
     // TODO - Can we move this somewhere else?  ordering of settings is causing this to get borked.
@@ -72,7 +79,7 @@ private[sbt] object BuildDef:
         case _                        => "default"
       }
     },
-    autoGeneratedProject := true
+    autoGeneratedProject := true,
   )
 
   def analyzed(

main/src/main/scala/sbt/internal/Load.scala

@@ -1061,7 +1061,7 @@ private[sbt] object Load {
                   val refs = existingIds.map(id => ProjectRef(buildUri, id))
                   if (discovered.isEmpty || java.lang.Boolean.getBoolean("sbt.root.ivyplugin"))
                     BuildDef.defaultAggregatedProject(defaultID, buildBase, refs)
-                  else BuildDef.generatedRootWithoutIvyPlugin(defaultID, buildBase, refs)
+                  else BuildDef.generatedRootSkipPublish(defaultID, buildBase, refs)
                 }
                 (root, false, Nil, otherProjects)
           val (finalRoot, projectLevelExtra) =

sbt-app/src/sbt-test/dependency-management/parent-skip-publish/build.sbt

@@ -0,0 +1,11 @@
+ThisBuild / organization := "com.example"
+ThisBuild / ivyPaths := IvyPaths((ThisBuild / baseDirectory).value.toString, Some(((ThisBuild / baseDirectory).value / "ivy" / "cache").toString))
+
+name := "root"
+
+lazy val core = project
+  .settings(
+    name := "core",
+    // organization := "com.example",
+    ivyPaths := IvyPaths((ThisBuild / baseDirectory).value.toString, Some(((ThisBuild / baseDirectory).value / "ivy" / "cache").toString))
+  )

sbt-app/src/sbt-test/dependency-management/parent-skip-publish/test

@@ -0,0 +1,3 @@
+> publishLocal
+
+$ absent ivy/cache/local/com.example/root_3/0.1.0-SNAPSHOT/poms/root_3.pom