Revert _log_skipped_link() optimization (#13333)

The addition of if not logger.isEnabledFor(logging.DEBUG) in
_log_skipped_link() means that skipped links are not stored, preventing
requires_python_skipped_reasons() from ever returning anything.

Author: ichard26

news/13333.bugfix.rst

@@ -0,0 +1,2 @@
+Fix regression that suppressed errors indicating which packages were ignored
+due to incompatible ``requires-python`` metadata.

src/pip/_internal/index/package_finder.py

@@ -732,11 +732,6 @@ def _sort_links(self, links: Iterable[Link]) -> List[Link]:
         return no_eggs + eggs
 
     def _log_skipped_link(self, link: Link, result: LinkType, detail: str) -> None:
-        # This is a hot method so don't waste time hashing links unless we're
-        # actually going to log 'em.
-        if not logger.isEnabledFor(logging.DEBUG):
-            return
-
         entry = (link, result, detail)
         if entry not in self._logged_links:
             # Put the link at the end so the reason is more visible and because