Issue: The Maintenance: Clear Cache page does not display the correct number + size of cached files.

This PR corrects the Number of Files on the Maintenance: Clear Cache page.

Summary of Changes

When using Joomla's System - Page Cache plugin, an /administrator/cache/page folder with index.html file is created. When you visit one page on the front-end, you will cache one page.
However, the Maintenance: Clear Cache page shows 2 files under Number of Files because it also counts the index.html file (which is not a cached file). It's confusing to see that number.

Testing Instructions

1. Switch on Joomla's System - Page Cache plugin

2. Goto the front-end and open one page. The Maintenance: Clear Cache counts 2 files.
3. Open the website files, e.g. using an FTP client like FileZilla.
   You'll see just one cached file and the index.html.

Actual result BEFORE applying this Pull Request

You'll see too many cached files under Number of Files (and Size) because it includes the index.html:

Expected result AFTER applying this Pull Request

You'll see the real number of cached files + size because the index.html is not counted as cache anymore:

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed