fix(medusa-plugin-brightpearl): account for shipping prices being tax inclusive (#2536)

**What**
BP plugin was recording total shipping price based on the shipping_method.price; however, this value may be with or without taxes depending on the tax inclusivity setting. This change ensures that the shipping price is calculated correctly.

.changeset/chilled-ads-flash.md

@@ -0,0 +1,5 @@
+---
+"medusa-plugin-brightpearl": patch
+---
+
+fix(medusa-plugin-brightpearl): account for shipping prices being tax inclusive