Make it work with the export_sources method

Contributes to CURA-10317

conanfile.py

@@ -218,7 +218,7 @@ class CuraConan(ConanFile):
         # Collect all dll's from PyQt6 and place them in the root
         binaries.extend([(f"{p}", ".") for p in Path(self._site_packages, "PyQt6", "Qt6").glob("**/*.dll")])
 
-        with open(os.path.join(self.recipe_folder, "UltiMaker-Cura.spec.jinja"), "r") as f:
+        with open(os.path.join(self.source_folder, "UltiMaker-Cura.spec.jinja"), "r") as f:
             pyinstaller = Template(f.read())
 
         version = self.conf_info.get("user.cura:version", default = self.version, check_type = str)