Set renovate schedule to monthly (#2401)

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## Related Issue

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- None

<!-- Fixes #0000 -->

## Summary

<!-- Please brief explanation of the changes made -->

- renovate 주기를 1달 단위로 조정합니다. 

## Details

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- 파싱이 잘 되는지 안되는지 로컬에서 테스트하기가 어려워서, 이렇게 해보고 다음주 월요일에 잘 되는지 봐야할 것 같습니다.
[@breejs/later](https://breejs.github.io/later/parsers.html#text) 파싱 로직에
**대부분** 의존한다고 하는데, 막상 매주 월요일로 잘 설정된 현재 값을 넣고 파싱하면 에러를 뱉습니다. 잘 안되면 cron
syntax로 해야할 것 같네요.

### Breaking change? (Yes/No)

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- No

## References

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aware of -->

- https://docs.renovatebot.com/configuration-options/#schedule

renovate.json

@@ -2,7 +2,7 @@
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": ["config:base", ":labels(chore:deps)"],
   "timezone": "Asia/Seoul",
-  "schedule": "on Monday after 10am before 7pm",
+  "schedule": "on Monday after 10am before 7pm every month",
   "packageRules": [
     {
       "groupName": "style",