Allow tests to pass in environments where NO_COLOR=1 is set (#777)

Co-authored-by: Michał Górny <mgorny@gentoo.org>

tests/conftest.py

@@ -0,0 +1,8 @@
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def reset_color_envvars(monkeypatch):
+    """Remove color-related envvars to fix test output"""
+    monkeypatch.delenv("FORCE_COLOR", raising=False)
+    monkeypatch.delenv("NO_COLOR", raising=False)