Make time-machine an optional dependency as intended

Author: Secrus

pyproject.toml

@@ -20,6 +20,10 @@ classifiers = [
 dependencies = [
     "python-dateutil>=2.6",
     "tzdata>=2020.1",
+]
+
+[project.optional-dependencies]
+test = [
     'time-machine>=2.6.0; implementation_name != "pypy"',
 ]