build: Switch build backend to PDM (again)

Seems PDM is the only build backend allowing one to supply package version externally without writing version string somewhere. setuptools_scm forces version change if repository is modified.

pyproject.toml

@@ -1,8 +1,8 @@
 #:schema https://json.schemastore.org/pyproject.json
 
 [build-system]
-requires = ['setuptools >= 64', 'setuptools_scm ~= 8.0']
-build-backend = 'setuptools.build_meta'
+requires = ['pdm-backend ~= 2.3']
+build-backend = 'pdm.backend'
 
 [project]
 name = 'types-lxml'
@@ -58,10 +58,13 @@ includes = [
 ]
 excludes = [
     '**/*.bak',
+    '*.patch',
+    '*.py',
+    '**/.mypy_cache',
+    '**/.pytest_cache',
 ]
 source-includes = [
-    'LICENSE',
-    'README.md',
+    'requirements.txt',
     'test-rt/',
     'test-stub/',
     'tox.ini',

tox.ini

@@ -60,6 +60,8 @@ package = skip
 commands = pyright {posargs:lxml-stubs}
 
 [testenv:build]
+passenv =
+    PDM_BUILD_SCM_VERSION
 deps =
     build
 package = skip