Do not save pip cache when using CACHED_ENVIRONMENT

Saving these files in the tarfile will push/pull on every build and
it's useless because if we are saving the environment already, these
packages will be already installed there. So, there is no need to keep
them in the tarfile to not use them after all.

Author: humitos

readthedocs/doc_builder/python_environments.py

@@ -129,15 +129,17 @@ def _pip_cache_cmd_argument(self):
 
         The decision is made considering if the directories are going to be
         cleaned after the build (``RTD_CLEAN_AFTER_BUILD=True`` or project has
-        the ``CLEAN_AFTER_BUILD`` feature enabled) and project has not the
-        feature ``CACHED_ENVIRONMENT``. In this case, there is no need to cache
+        the ``CLEAN_AFTER_BUILD`` feature enabled) or project has the feature
+        ``CACHED_ENVIRONMENT``. In this case, there is no need to cache
         anything.
         """
         if (
-            (
-                settings.RTD_CLEAN_AFTER_BUILD or
-                self.project.has_feature(Feature.CLEAN_AFTER_BUILD)
-            ) and not self.project.has_feature(Feature.CACHED_ENVIRONMENT)
+            # Cache is going to be removed anyways
+            settings.RTD_CLEAN_AFTER_BUILD or
+            self.project.has_feature(Feature.CLEAN_AFTER_BUILD) or
+            # Cache will be pushed/pulled each time and won't be used because
+            # packages are already installed in the environment
+            self.project.has_feature(Feature.CACHED_ENVIRONMENT)
         ):
             return [
                 '--no-cache-dir',