Update Renovate config to ignore JUnit 6 which requires Java 17+ (#14848)

Author: trask

.github/renovate.json5

@@ -112,6 +112,16 @@
         'io.opentelemetry:{/,}**',
       ],
     },
+    {
+      // junit 6+ requires Java 17+
+      matchPackageNames: [
+        'org.junit:**',
+      ],
+      matchUpdateTypes: [
+        'major',
+      ],
+      enabled: false,
+    },
     {
       // junit-pioneer 2+ requires Java 11+
       matchPackageNames: [