* Let's see if the tests now pass against PHP8; output file looks to be good
* Font can't be both superscript and subscript at the same time, so we use if/else rather than if/if
* Pattern Fill style should default to 'solid' if there is a pattern fill style for a conditional; though may need to check if there are defined fg/bg colours as well; and only set a fill style if there are defined colurs
Openpyxl can generate the xml tag `<patternFill/>`, possibly even as a default style. Excel has no problem with this, treating it as "fill none", but PhpSpreadsheet has a glitch because it treats it as "fill solid white". So, when PhpSpreadsheet loads and saves such a file, the result at first appears as if gridlines are disabled; in fact, the gridlines are merely invisible behind the cells with their solid white fill. This PR makes PhpSpreadsheet behave the same as Excel in this circumstance.
Co-authored-by: Mark Baker <mark@lange.demon.co.uk>
Mark Baker
oleibman