Fix typo in tune-output.rst (ray-project#37506)

Signed-off-by: David Yoonsik Yoo <yu.david880@gmail.com>
Signed-off-by: NripeshN <nn2012@hw.ac.uk>

doc/source/tune/tutorials/tune-output.rst

@@ -324,7 +324,7 @@ You can create a custom logger by inheriting the LoggerCallback interface (:ref:
     class CustomLoggerCallback(LoggerCallback):
         """Custom logger interface"""
 
-        def __init__(self, filename: str = "log.txt):
+        def __init__(self, filename: str = "log.txt"):
             self._trial_files = {}
             self._filename = filename