Fix running debuggers inside airflow tasks test (#26806)

As part of 2.3.3 we added redaction to output from the tasks test
command, but unfortunately that broke using a debugger with this error:

```
  File "/usr/lib/python3.10/pdb.py", line 262, in user_line
    self.interaction(frame, None)
  File "/home/ash/.virtualenvs/airflow/lib/python3.10/site-packages/pdb.py", line 231, in interaction
    self._cmdloop()
  File "/usr/lib/python3.10/pdb.py", line 322, in _cmdloop
    self.cmdloop()
  File "/usr/lib/python3.10/cmd.py", line 126, in cmdloop
    line = input(self.prompt)
TypeError: 'NoneType' object cannot be interpreted as an integer
```

(ipdb has a similar but different error)

The "fix" is to assign a fileno attribute to the object. `input()` needs
this to write the prompt. It feels like a "bug" that it doesn't work
without it, but as this class is only used in `tasks test` this is a
safe change

airflow/utils/log/secrets_masker.py

@@ -271,6 +271,7 @@ class RedactedIO(TextIO):
 
     def __init__(self):
         self.target = sys.stdout
+        self.fileno = sys.stdout.fileno
 
     def write(self, s: str) -> int:
         s = redact(s)

tests/utils/log/test_secrets_masker.py

@@ -18,9 +18,11 @@
 
 import contextlib
 import inspect
+import io
 import logging
 import logging.config
 import os
+import sys
 import textwrap
 
 import pytest
@@ -363,3 +365,13 @@ def test_write(self, capsys):
         RedactedIO().write(p)
         stdout = capsys.readouterr().out
         assert stdout == "***"
+
+    def test_input_builtin(self, monkeypatch):
+        """
+        Test that when redirect is inplace the `input()` builtin works.
+
+        This is used by debuggers!
+        """
+        monkeypatch.setattr(sys, 'stdin', io.StringIO("a\n"))
+        with contextlib.redirect_stdout(RedactedIO()):
+            assert input() == "a"