Maven publication: Produce correct <scm><tag> in pom.xml

`project.scm.tag` in a Maven pom is intended to refer to the SCM (Git) tag. We currently publish `main`, which is incorrect.

This change omits the SCM tag for snapshot builds, but emits the Git tag for releases.

Author: snazy

build-logic/src/main/kotlin/publishing/configurePom.kt

@@ -103,7 +103,10 @@ internal fun configurePom(project: Project, mavenPublication: MavenPublication,
               connection.set("scm:git:$codeRepo")
               developerConnection.set("scm:git:$codeRepo")
               url.set("$codeRepo/tree/main")
-              tag.set("main")
+              val version = project.version.toString()
+              if (!version.endsWith("-SNAPSHOT")) {
+                tag.set("apache-polaris-$version")
+              }
             }
             issueManagement { url.set(projectPeople.bugDatabase) }