Make time-machine an optional dependency as intended

Author: Secrus

pyproject.toml

@@ -22,10 +22,14 @@ dependencies = [
     "python-dateutil>=2.6",
     "tzdata>=2020.1",
     'backports.zoneinfo>=0.2.1; python_version < "3.9"',
-    'time-machine>=2.6.0; implementation_name != "pypy"',
     'importlib-resources>=5.9.0; python_version < "3.9"'
 ]
 
+[project.optional-dependencies]
+test = [
+    'time-machine>=2.6.0; implementation_name != "pypy"',
+]
+
 [project.urls]
 Homepage = "https://pendulum.eustace.io"
 Documentation = "https://pendulum.eustace.io/docs"