ci(renovate): update indirect deps only for hugo

Updating indirect dependencies in the main go.mod does not make sense as
they are not being used and are reverted by running go mod tidy.

Signed-off-by: Michael Adler <michael.adler@siemens.com>

renovate.json5

@@ -35,8 +35,7 @@
       matchUpdateTypes: ["minor", "patch", "digest"],
     },
     {
-      // needed to maintain our hugo dependencies
-      matchManagers: ["gomod"],
+      matchFileNames: ["hugo/go.mod"],
       matchDepTypes: ["indirect"],
       enabled: true,
     },