Update pdfium_backend.py (close open documents)

Author: YB27

camelot/backends/pdfium_backend.py

@@ -41,3 +41,5 @@ def convert(self, pdf_path: str, png_path: str, resolution: int = 300) -> None:
         doc.init_forms()
         image = doc[0].render(scale=resolution / 72).to_pil()
         image.save(png_path)
+        image.close()
+        doc.close()