ci: fix dependabot config (#3041)

Missed one "never" in the last commit.

Signed-off-by: Terri Oda <[email protected]>

Author: terriko

.github/dependabot.yml

@@ -344,5 +344,5 @@ updates:
   - package-ecosystem: maven
     directory: /test/language_data
     schedule:
-      interval: never
+      interval: monthly