ci: group golang.org/x/ under golang dependencies

Golang dependencies are already grouped, but they only contain packages
from `github.com/golang*`. There are more Golang standard packages that
are located at `golang.org/x/*`. Because of the tight relationship
between these packages, it is more efficient to group updates together.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

.github/dependabot.yml

@@ -11,6 +11,7 @@ updates:
       golang-dependencies:
         patterns:
           - "github.com/golang*"
+          - "golang.org/x/*"
       k8s-dependencies:
         patterns:
           - "k8s.io*"