Improve --dry-run with legacy resolver

Author: sbidoul

src/pip/_internal/commands/install.py

@@ -356,7 +356,9 @@ def run(self, options: Values, args: List[str]) -> int:
             if options.dry_run:
                 would_install_items = sorted(
                     (r.metadata["name"], r.metadata["version"])
-                    for r in requirement_set.all_requirements
+                    # Use get_installation_order because it does some important
+                    # filtering with the legacy resolver.
+                    for r in resolver.get_installation_order(requirement_set)
                 )
                 if would_install_items:
                     write_output(