[AIRFLOW-3183] Fix bug in DagFileProcessorManager.max_runs_reached() (apache#4031)

The condition is intended to ensure the function
will return False if any file's run_count is still smaller
than max_run. But the operator used here is "!=".
Instead, it should be "<".

This is because in DagFileProcessorManager,
there is no statement helping limit the upper
limit of run_count. It's possible that
files' run_count will be bigger than max_run.
In such case, max_runs_reached() method
may fail its purpose.

Author: XD-DENG

airflow/utils/dag_processing.py

@@ -578,7 +578,7 @@ def max_runs_reached(self):
         if self._max_runs == -1:  # Unlimited runs.
             return False
         for file_path in self._file_paths:
-            if self._run_count[file_path] != self._max_runs:
+            if self._run_count[file_path] < self._max_runs:
                 return False
         if self._run_count[self._heart_beat_key] < self._max_runs:
             return False