[MNG-8229] CI Friendly versions confuse model pool

Fixing the method (there is one GA inside reactor),
but this still does not fix the issue, now it fails
elsewhere.

The problem in short is CI friendly version and its
half-assed solution as model version "suddenly" change
from file-activated models to effective ones.

---

https://issues.apache.org/jira/browse/MNG-8229

maven-core/src/main/java/org/apache/maven/project/ReactorModelPool.java

@@ -19,6 +19,7 @@
 package org.apache.maven.project;
 
 import java.nio.file.Path;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Map;
@@ -48,13 +49,20 @@ class ReactorModelPool {
      * @throws IllegalStateException if version was null and multiple modules share the same groupId + artifactId
      */
     public Model get(String groupId, String artifactId, String version) {
-        return modelsByGa.getOrDefault(new GAKey(groupId, artifactId), Collections.emptySet()).stream()
-                .filter(m -> version == null || version.equals(getVersion(m)))
-                .reduce((a, b) -> {
-                    throw new IllegalStateException(
-                            "Multiple modules with key " + a.getGroupId() + ':' + a.getArtifactId());
-                })
-                .orElse(null);
+        Collection<Model> models = modelsByGa.getOrDefault(new GAKey(groupId, artifactId), Collections.emptySet());
+        if (models.isEmpty()) {
+            return null;
+        } else if (models.size() == 1) {
+            return models.iterator().next();
+        } else {
+            return models.stream()
+                    .filter(m -> version == null || version.equals(getVersion(m)))
+                    .reduce((a, b) -> {
+                        throw new IllegalStateException(
+                                "Multiple modules with key " + a.getGroupId() + ':' + a.getArtifactId());
+                    })
+                    .orElse(null);
+        }
     }
 
     private String getVersion(Model model) {