Configure pyupgrade in pre-commit and Tox

The 'types: [python]' option in pre-commit configuration is needed in
order to avoid pyupgrade to operate on non-Python files, e.g.
'rpm/build' (not sure why it does so).

.pre-commit-config.yaml

@@ -0,0 +1,8 @@
+repos:
+- repo: local
+  hooks:
+    - id: pyupgrade
+      name: pyupgrade
+      entry: pyupgrade --py39-plus --exit-zero-even-if-changed
+      language: system
+      types: [python]

MANIFEST.in

@@ -1,5 +1,6 @@
 include .coveragerc
 include .flake8
+include .pre-commit-config.yaml
 include pyproject.toml
 include *.md
 include *.txt

pyproject.toml

@@ -35,6 +35,7 @@ lint = [
     "check-manifest",
     "flake8",
     "isort",
+    "pyupgrade",
 ]
 typing = [
     "mypy",

tox.ini

@@ -8,12 +8,15 @@ commands=
   flake8
   black --check --diff .
   isort --check --diff .
+  pre-commit run --all-files --show-diff-on-failure pyupgrade
   check-manifest
 deps =
   flake8
   black
   check-manifest
   isort
+  pre-commit
+  pyupgrade
 skip_install = true
 
 [testenv:tests{,-ci}]