Group the google/x renovabot upgrades (#5813)

Based on the suggestion in #5811.

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>

renovate.json

@@ -23,6 +23,10 @@
     {
       "matchPackageNames": ["google.golang.org/genproto/googleapis/**"],
       "groupName": "googleapis"
+    },
+    {
+      "matchPackageNames": ["golang.org/x/**"],
+      "groupName": "golang.org/x"
     }
   ]
 }