Add warn_tag="deprecated" to unix_path_package_info_legacy warning message (#18233)

Changelog: Omit
Docs: Omit

Closes #18232

Author: memsharded

conan/tools/microsoft/subsystems.py

@@ -10,5 +10,5 @@ def unix_path_package_info_legacy(conanfile, path, path_flavor=None):
     message = "The use of 'unix_path_legacy_compat' is deprecated in Conan 2.0 and does not " \
               "perform path conversions. This is retained for compatibility with Conan 1.x " \
               "and will be removed in a future version."
-    conanfile.output.warning(message)
+    conanfile.output.warning(message, warn_tag="deprecated")
     return path