Fix license deprecation warning

Author: antonwolfy

pyproject.toml

@@ -66,7 +66,8 @@ keywords = [
   "gpu",
   "dpcpp"
 ]
-license = {text = "Apache 2.0"}
+license = "Apache 2.0"
+license-files = ["LICENSE.txt"]
 maintainers = [{name = "Intel Corporation"}]
 name = "dpnp"
 readme = {file = "README.md", content-type = "text/markdown"}