pyproject: fix the declared Python floor and the license form

Two metadata defects, left untouched by #22 because both depend on
what the project is supported on rather than on what the code
tolerates.

requires-python claimed ">=3.6". The package cannot run on 3.6:
check.py and ovs.py call subprocess.run with capture_output, an
argument added in 3.7, so system_check and clear_ovs raise TypeError
there. The real floor is at least 3.7, and 3.7 and 3.8 are both end of
life and absent from the GitHub runners, so neither can be tested.
Declare ">=3.9", the lowest version the CI matrix actually verifies.
Every live deployment target is above it: Debian trixie ships 3.13,
Yocto wrynose 3.14, and the oldest manifest still around, kirkstone,
3.10.

license was a TOML table, which setuptools deprecates in favour of a
plain SPDX expression. The build printed a SetuptoolsDeprecationWarning
on every run announcing removal by 2027-02-18. Use the string form
together with license-files, and raise the build-system requirement to
setuptools 77, the release that introduced both.

The metadata now says License-Expression: Apache-2.0 under
Metadata-Version 2.4, and the LICENSE file is still shipped in the
wheel. The build is warning-free and stays byte-for-byte reproducible
under SOURCE_DATE_EPOCH.

The setuptools bump is safe for the two maintained targets, which is
what matters here: both Ansible roles install with
--no-build-isolation, so build-system requires is not honoured on
target and the setuptools already present is the one that counts.
Debian trixie ships 78.1.1 and Yocto wrynose 82.0.1, both above 77.

Signed-off-by: Florent Carli <florent.carli@rte-france.com>

Author: insatomcat

pyproject.toml

@@ -9,9 +9,10 @@ authors = [
     { name = "Florent Carli", email = "florent.carli@rte-france.com" },
     { name = "Mathieu Dupré", email = "mathieu.dupre@savoirfairelinux.com" }
 ]
-license = { text = "Apache-2.0" }
+license = "Apache-2.0"
+license-files = ["LICENSE"]
 readme = "README.md"
-requires-python = ">=3.6"
+requires-python = ">=3.9"
 dependencies = [
     "PyYAML",
 ]
@@ -30,7 +31,7 @@ setup_ovs = "setup_ovs.setup_ovs:main"
 Homepage = "https://github.com/seapath/python3-setup-ovs"
 
 [build-system]
-requires = ["setuptools>=61", "wheel"]
+requires = ["setuptools>=77"]
 build-backend = "setuptools.build_meta"
 
 [tool.pytest.ini_options]