Tweak for AMORDEGRC

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 #3897. Then someone reported a problem (not specifically related to Php8.4) with TRUNC. That was fixed by PR #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.

src/PhpSpreadsheet/Calculation/Financial/Amortization.php

@@ -9,8 +9,6 @@
 
 class Amortization
 {
-    private const ROUNDING_ADJUSTMENT = (PHP_VERSION_ID < 80400) ? 0 : 1e-14;
-
     /**
      * AMORDEGRC.
      *
@@ -82,7 +80,7 @@ public static function AMORDEGRC(
         $amortiseCoeff = self::getAmortizationCoefficient($rate);
 
         $rate *= $amortiseCoeff;
-        $rate += self::ROUNDING_ADJUSTMENT;
+        $rate = (float) (string) $rate; // ugly way to avoid rounding problem
         $fNRate = round($yearFrac * $rate * $cost, 0);
         $cost -= $fNRate;
         $fRest = $cost - $salvage;