Changes to Php8.4 floating point calculations caused failures in unit tests for ROUNDDOWN, ROUNDUP, and AMORDEGRC. These were addressed in a kludgey manner by PR PHPOffice#3897. Then someone reported a problem (not specifically related to Php8.4) with TRUNC. That was fixed by PR PHPOffice#4115, in which I applied the method used by TRUNC to ROUNDDOWN and ROUNDUP as well. The method used to fix these was to cast a floating point value to string and then cast it back to float again. It's a bit surprising that this works, but it seems effective for all our test cases, and is less kludgey than what had been done earlier. Missing from that PR was a similar change for AMORDEGRC. This PR applies that change to AMORDEGRC, which again passes the unit test suite for all releases of Php.