[2.x] fix: Populate explicitArtifacts from classifier in UpdateReport (#8874)

**Problem**
When a dependency is declared with a classifier (e.g., classifier "linux-x86_64"),
the UpdateReport > ModuleReport.module.explicitArtifacts is empty. The classifier
data is available as Publication objects during Coursier resolution but is lost
when SbtUpdateReport reconstructs the ModuleID.

**Solution**
In SbtUpdateReport.moduleReport, extract explicit artifacts from Publications
with non-empty classifiers and apply them to the ModuleID used by ModuleReport.
This is done on a per-report copy to avoid mutating the shared moduleId cache.

Fixes #5491

lm-coursier/src/main/scala/lmcoursier/internal/SbtUpdateReport.scala

@@ -95,6 +95,18 @@ private[internal] object SbtUpdateReport {
       artifact((dependency.module, infoProperties(project).toMap, pub, artifact0, classLoaders))
     }
 
+    val explicitArts = artifacts
+      .collect {
+        case (pub, _, _) if pub.classifier.nonEmpty =>
+          sbt.librarymanagement
+            .Artifact(pub.name)
+            .withType(pub.`type`.value)
+            .withExtension(pub.ext.value)
+            .withClassifier(Some(pub.classifier.value))
+      }
+      .distinct
+      .toVector
+
     val publicationDate = project.info.publication.map { dt =>
       new GregorianCalendar(dt.year, dt.month, dt.day, dt.hour, dt.minute, dt.second)
     }
@@ -113,8 +125,13 @@ private[internal] object SbtUpdateReport {
       )
     }
 
+    val modId = moduleId((dependency, project.version, infoProperties(project).toMap))
+    val modIdWithArts =
+      if explicitArts.nonEmpty then modId.withExplicitArtifacts(explicitArts)
+      else modId
+
     val rep = ModuleReport(
-      moduleId((dependency, project.version, infoProperties(project).toMap)),
+      modIdWithArts,
       sbtArtifacts.toVector,
       sbtMissingArtifacts.toVector
     )

sbt-app/src/sbt-test/dependency-management/classifier-report/build.sbt

@@ -0,0 +1,17 @@
+lazy val check = taskKey[Unit]("check classifier in update report")
+
+lazy val root = (project in file(".")).settings(
+  scalaVersion := "2.13.16",
+  libraryDependencies += "io.netty" % "netty-transport-native-epoll" % "4.1.118.Final" classifier "linux-x86_64",
+  check := {
+    val report = update.value
+    val modules = report.configurations.flatMap(_.modules)
+    val nettyModule = modules.find(_.module.name == "netty-transport-native-epoll")
+      .getOrElse(sys.error("netty-transport-native-epoll not found in update report"))
+    val explicitArts = nettyModule.module.explicitArtifacts
+    assert(explicitArts.nonEmpty, s"Expected non-empty explicitArtifacts, got: $explicitArts")
+    val classifiers = explicitArts.flatMap(_.classifier)
+    assert(classifiers.contains("linux-x86_64"),
+      s"Expected classifier 'linux-x86_64' in explicitArtifacts, got: $classifiers")
+  },
+)

sbt-app/src/sbt-test/dependency-management/classifier-report/test

@@ -0,0 +1 @@
+> check