Do not use the .php extension in mtime protected storage to work around bogus PHP extensions

This issue is being reviewed by the kind folks in Slack, #needs-review-queue-initiative. We are working to keep the size of Needs Review queue [2700+ issues] to around 400 (1 month or less), following Review a patch or merge request → as a guide.

Know it seems difficult to pinpoint the steps to reproduce but think we will really need them before moving forward. Still needs security review though.

As we've not had any further reports of this in over a year, it seems likely the problem is resolved and Drupal core does not need to make any changes.

Marking as postponed for now; if there are no further reports within six months then I think this issue can be closed.

No more reports in two years, closing as outdated.