Fix running tests in environment with FORCE_COLOR or NO_COLOR set

Ensure to unset FORCE_COLOR and NO_COLOR environment variables within
the scope of individual tests, in order to fix test failures when these
variables are set in the environment where tests are run, e.g. via:

    NO_COLOR=1 tox

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed
+
+- Running tests in environment with `FORCE_COLOR` or `NO_COLOR` environment variables
+
 ## [13.7.0] - 2023-11-15
 
 ### Added

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)