ruff: Use more specific name to enable pyupgrade rule

UP is the exact name of the rule, instead of U. Use the exact name to
avoid potential problems caused by any UX rules which can be added
in the future.

Change-Id: I5fa59181fcd3e28bf3c87ce2a5e610561b2ee8a8
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

Author: kajinamit

pyproject.toml

@@ -748,7 +748,7 @@ quote-style = "preserve"
 docstring-code-format = true
 
 [tool.ruff.lint]
-select = ["E4", "E7", "E9", "F", "S", "U"]
+select = ["E4", "E7", "E9", "F", "S", "UP"]
 
 [tool.ruff.lint.per-file-ignores]
 "openstackclient/tests/*" = ["S"]