ci(dependabot): Change interval for npm to monthly (#1424)

npm packages are used for website only in this repo. Consider that
golangci-lint normally releases once a month, this commit is to change
interval for npm dependabot from weekly to monthly.

Main benefits could be:

- Reduce the noise for maintainers
- Improve generated CHANGELOG.
These changes are not useful for end users.

Signed-off-by: Tam Mach <[email protected]>

Author: sayboras

.github/dependabot.yml

@@ -30,6 +30,6 @@ updates:
   - package-ecosystem: npm
     directory: "/docs"
     schedule:
-      interval: weekly
+      interval: monthly
     reviewers:
       - "golangci/team"