[SEDONA-496] Dependabot: reduce the open pull requests limit to 2 (#1238

)

This will reduce the number of open pull requests for version updates at any one time.

Might help to reduce spam like content on the mailing list.

https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#open-pull-requests-limit

.github/dependabot.yml

@@ -2,10 +2,12 @@ version: 2
 updates:
   - package-ecosystem: github-actions
     directory: /
+    open-pull-requests-limit: 2
     schedule:
       interval: monthly
 
   - package-ecosystem: pip
     directory: /docker/sedona-spark-jupyterlab
+    open-pull-requests-limit: 2
     schedule:
       interval: monthly