Update Renovate config to ignore JUnit 6 which requires Java 17+ (open-telemetry#7718)

Author: trask

.github/renovate.json5

@@ -31,6 +31,16 @@
       ignoreUnstable: false,
       allowedVersions: '!/\\-SNAPSHOT$/',
     },
+    {
+      // junit 6+ requires Java 17+
+      matchPackageNames: [
+        'org.junit:**',
+      ],
+      matchUpdateTypes: [
+        'major',
+      ],
+      enabled: false,
+    },
     {
       // junit-pioneer 2+ requires Java 11+
       matchPackageNames: [