fix(maven): Default group ID for plugins (#5102)

Co-authored-by: Michael Kriese <michael.kriese@visualon.de>

lib/manager/maven/extract.ts

@@ -32,9 +32,14 @@ interface MavenProp {
 
 function depFromNode(node: XmlElement): PackageDependency | null {
   if (!node.valueWithPath) return null;
-  const groupId = node.valueWithPath('groupId');
+  let groupId = node.valueWithPath('groupId');
   const artifactId = node.valueWithPath('artifactId');
   const currentValue = node.valueWithPath('version');
+
+  if (!groupId && node.name === 'plugin') {
+    groupId = 'org.apache.maven.plugins';
+  }
+
   if (groupId && artifactId && currentValue) {
     const depName = `${groupId}:${artifactId}`;
     const versionNode = node.descendantWithPath('version');

test/manager/maven/__snapshots__/extract.spec.ts.snap

@@ -34,6 +34,16 @@ Object {
         "https://maven.atlassian.com/content/repositories/atlassian-public/",
       ],
     },
+    Object {
+      "currentValue": "2.4.2",
+      "datasource": "maven",
+      "depName": "org.apache.maven.plugins:maven-release-plugin",
+      "fileReplacePosition": 1287,
+      "registryUrls": Array [
+        "https://repo.maven.apache.org/maven2",
+        "https://maven.atlassian.com/content/repositories/atlassian-public/",
+      ],
+    },
     Object {
       "currentValue": "1.8.1",
       "datasource": "maven",

test/manager/maven/__snapshots__/index.spec.ts.snap

@@ -35,6 +35,16 @@ Array [
           "https://maven.atlassian.com/content/repositories/atlassian-public/",
         ],
       },
+      Object {
+        "currentValue": "2.4.2",
+        "datasource": "maven",
+        "depName": "org.apache.maven.plugins:maven-release-plugin",
+        "fileReplacePosition": 1287,
+        "registryUrls": Array [
+          "https://repo.maven.apache.org/maven2",
+          "https://maven.atlassian.com/content/repositories/atlassian-public/",
+        ],
+      },
       Object {
         "currentValue": "1.8.1",
         "datasource": "maven",