[airflow] Improve the AIR002 error message (#20173)

<!--
Thank you for contributing to Ruff/ty! To help us out with reviewing,
please consider the following:

- Does this pull request include a summary of the change? (See below.)
- Does this pull request include a descriptive title? (Please prefix
with `[ty]` for ty pull
  requests.)
- Does this pull request include references to any relevant issues?
-->

## Summary

<!-- What's the purpose of the change? What does it do, and why? -->


### What
Change the message from "DAG should have an explicit `schedule`
argument" to "`DAG` or `@dag` should have an explicit `schedule`
argument"

### Why
We're trying to get rid of the idea that DAG in airflow was Directed
acyclic graph. Thus, change it to refer to the class `DAG` or the
decorator `@dag` might help a bit.

## Test Plan

<!-- How was it tested? -->

update the test fixtures accordly

crates/ruff_linter/src/rules/airflow/rules/dag_schedule_argument.rs

@@ -46,7 +46,7 @@ pub(crate) struct AirflowDagNoScheduleArgument;
 impl Violation for AirflowDagNoScheduleArgument {
     #[derive_message_formats]
     fn message(&self) -> String {
-        "DAG should have an explicit `schedule` argument".to_string()
+        "`DAG` or `@dag` should have an explicit `schedule` argument".to_string()
     }
 }
 

crates/ruff_linter/src/rules/airflow/snapshots/ruff_linter__rules__airflow__tests__AIR002_AIR002.py.snap

@@ -1,7 +1,7 @@
 ---
 source: crates/ruff_linter/src/rules/airflow/mod.rs
 ---
-AIR002 DAG should have an explicit `schedule` argument
+AIR002 `DAG` or `@dag` should have an explicit `schedule` argument
  --> AIR002.py:4:1
   |
 2 | from airflow.timetables.simple import NullTimetable
@@ -12,7 +12,7 @@ AIR002 DAG should have an explicit `schedule` argument
 6 | DAG(dag_id="class_schedule", schedule="@hourly")
   |
 
-AIR002 DAG should have an explicit `schedule` argument
+AIR002 `DAG` or `@dag` should have an explicit `schedule` argument
   --> AIR002.py:13:2
    |
 13 | @dag()