pdm-pep517 is deprecated

[0-wiz-0]

https://pypi.org/project/pdm-pep517/ says:

This project has been renamed and re-published as [pdm-backend](https://pypi.org/project/pdm-backend)

Here's a minimal diff to switch:

--- pyproject.toml.orig 2023-03-09 10:01:30.924441300 +0000
+++ pyproject.toml
@@ -38,9 +38,9 @@ cmake-language-server = "cmake_language_

 [build-system]
 requires = [
-    "pdm-pep517>=1.0.0",
+    "pdm-backend>=1.0.0",
 ]
-build-backend = "pdm.pep517.api"
+build-backend = "pdm.backend"

 [tool.pdm.version]
 source = "scm"