build(Gradle): Fix publishing the gradle-model artifact

This needs to be published as it is not only a dependency of the
embedded `gradle-plugin`, but also of the `gradle-inspector` and the
"legacy" `gradle-package-manager`, see how [1] refers to it (under the
wrong group name, as publishing conventions were not applied so far).

[1]: https://repo.maven.apache.org/maven2/org/ossreviewtoolkit/plugins/package-managers/2.0.0/package-managers-2.0.0.pom

Signed-off-by: Sebastian Schuberth <[email protected]>

Author: sschuberth

plugins/package-managers/gradle-model/build.gradle.kts

@@ -20,4 +20,5 @@
 plugins {
     // Apply precompiled plugins.
     id("ort-kotlin-conventions")
+    id("ort-publication-conventions")
 }