Infra: Run dependabot check weekly (#1850)

<!--
Thanks for opening a pull request!
-->

<!-- In the case this PR will resolve an issue, please replace
${GITHUB_ISSUE_ID} below with the actual Github issue id. -->
<!-- Closes #${GITHUB_ISSUE_ID} -->
Closes #1815

# Rationale for this change
We have a lot of dependabot commits (in the 0.9.0 release, 148 commits
were from contributors and 95 from Dependabot)

Dependabot config doc
https://docs.github.com/en/code-security/dependabot/working-with-dependabot/dependabot-options-reference#required-keys

# Are these changes tested?
yes

# Are there any user-facing changes?
no
<!-- In the case of user-facing changes, please add the changelog label.
-->

Author: kevinjqliu

.github/dependabot.yml

@@ -22,9 +22,9 @@ updates:
   - package-ecosystem: "pip"
     directory: "/"
     schedule:
-      interval: "daily"
+      interval: "weekly"
     open-pull-requests-limit: 50
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "daily"
+      interval: "weekly"