Allow `NURSERY` in JSON Schema (#7374)

## Summary

At some point, we removed these so that they wouldn't be autocompleted
for users, since we wanted to discourage usage of `ALL`. But given that
they're valid values, I think that was a bad idea -- it leads to an even
more confusing experience whereby JSON Schema validators tell you that
you have an error, when you don't.

Closes https://github.com/astral-sh/ruff/issues/7261.

crates/ruff/src/rule_selector.rs

@@ -254,8 +254,9 @@ mod schema {
                 instance_type: Some(InstanceType::String.into()),
                 enum_values: Some(
                     [
-                        // Include the non-standard "ALL" selector.
+                        // Include the non-standard "ALL" and "NURSERY" selectors.
                         "ALL".to_string(),
+                        "NURSERY".to_string(),
                         // Include the legacy "C" and "T" selectors.
                         "C".to_string(),
                         "T".to_string(),

ruff.schema.json

@@ -2161,6 +2161,7 @@
         "NPY001",
         "NPY002",
         "NPY003",
+        "NURSERY",
         "PD",
         "PD0",
         "PD00",