chore(nimbus): apply ruff format to WIN10_EXISTING_USERS_NEED_DEFAULT description

Because

* CI's ruff format --check was failing on the new targeting constant
  because the description string fit on one line.

This commit

* Collapses the multi-line description=(...) onto a single line so
  ruff format --check passes.

Author: jaredlockhart

experimenter/experimenter/targeting/constants.py

@@ -1168,9 +1168,7 @@ def __post_init__(self):
 WIN10_EXISTING_USERS_NEED_DEFAULT = NimbusTargetingConfig(
     name="Windows 10 existing users needing default",
     slug="win10_existing_users_need_default",
-    description=(
-        "Windows 10 users with profiles older than 28 days needing default"
-    ),
+    description=("Windows 10 users with profiles older than 28 days needing default"),
     targeting=f"{PROFILE28DAYS} && {WIN10_NEED_DEFAULT.targeting}",
     desktop_telemetry="",
     sticky_required=False,