Take into account the value of request parameter page for caching the…

[erral]

… generated sitemap

• I signed and returned the Plone Contributor Agreement, and received and accepted an invitation to join a team in the Plone GitHub organization.
• I verified there aren't any other open pull requests for the same change.
• I followed the guidelines in Contributing to Plone.
• I successfully ran code quality checks on my changes locally.
• I successfully ran tests on my changes locally.
• If needed, I added new tests for my changes.
• If needed, I added documentation for my changes.
• I included a change log entry in my commits.

---

In #382 I introduced the sitemap-index.xml here, to be aligned with latest changes in sitemap generation where search engines ignored sitemap files with lot of URLs.

The method that generates the sitemap is cached but it does not take the page parameter into account, so no matter which is the page you requested you are returned the first cached page.

This PR introduces the page parameter's value in the caching key .

[mister-roboto]

@erral thanks for creating this Pull Request and helping to improve Plone!

TL;DR: Finish pushing changes, pass all other checks, then paste a comment:

@jenkins-plone-org please run jobs

To ensure that these changes do not break other parts of Plone, the Plone test suite matrix needs to pass, but it takes 30-60 min. Other CI checks are usually much faster and the Plone Jenkins resources are limited, so when done pushing changes and all other checks pass either start all Jenkins PR jobs yourself, or simply add the comment above in this PR to start all the jobs automatically.

Happy hacking!

[erral]

@jenkins-plone-org please run jobs

[erral]

@jenkins-plone-org please run jobs

[thet]

LGTM. This targets Plone 6.3.
Ref: #446

[erral]

@jenkins-plone-org please run jobs