MkDocs: fix USE_MKDOCS_LATEST feature flag logic

The logic was inverted and we were installing old MkDocs version to projects
with `USE_MKDOCS_LATEST` feature flag.

Closes #10402

Author: humitos

readthedocs/doc_builder/python_environments.py

@@ -211,8 +211,8 @@ def install_core_requirements(self):
                     positive='mkdocs==0.17.3',
                     negative=self.project.get_feature_value(
                         Feature.USE_MKDOCS_LATEST,
-                        positive='mkdocs<1.1',
-                        negative='mkdocs',
+                        positive="mkdocs",
+                        negative="mkdocs<1.1",
                     ),
                 ),
             )