Mark tests needing TOML-writing library with a custom marker

This way they can be conveniently skipped with `pytest -m "not
tomlwrite"` in environments where such libraries aren't available.

stages/test/test_bootc_install_config.py

@@ -73,6 +73,7 @@ STAGE_NAME = "org.osbuild.bootc.install.config"
         )
     ]
 )
+@pytest.mark.tomlwrite
 def test_bootc_install_config(tmp_path, stage_module, options, expected_config):
     stage_module.main(tmp_path, options)
     # different toml libraries write out arrays in different ways (one line vs many), so we need to parse the result

stages/test/test_containers_storage_conf.py

@@ -18,6 +18,7 @@ TEST_INPUT = [
 STAGE_NAME = "org.osbuild.containers.storage.conf"
 
 
+@pytest.mark.tomlwrite
 @pytest.mark.parametrize("test_filename", ["/etc/containers/storage.conf", "/usr/share/containers/storage.conf"])
 @pytest.mark.parametrize("test_storage,test_options,expected", TEST_INPUT)
 def test_containers_storage_conf_integration(tmp_path, stage_module, test_filename, test_storage, test_options, expected):  # pylint: disable=unused-argument

test/conftest.py

@@ -17,3 +17,6 @@ def pytest_configure(config):
     # pylint: disable=global-statement
     global unsupported_filesystems
     unsupported_filesystems = config.getoption("--unsupported-fs")
+    config.addinivalue_line(
+        "markers", "tomlwrite: mark test to run only in an environment with a TOML-writing library available"
+    )

test/mod/test_util_toml.py

@@ -4,6 +4,8 @@
 import os
 from tempfile import TemporaryDirectory
 
+import pytest
+
 from osbuild.util import toml
 
 data_obj = {
@@ -26,6 +28,7 @@ str = "test"
 """
 
 
+@pytest.mark.tomlwrite
 def test_write_read():
     with TemporaryDirectory() as tmpdir:
         path = os.path.join(tmpdir, "test.toml")