minor #11879 Add caution about combining excluded_http_codes with passthru_level (rpkamp)

This PR was submitted for the 4.2 branch but it was merged into the 4.3 branch instead (closes #11879).

Discussion
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Add caution about combining excluded_http_codes with passthru_level

Commits
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d37c804 Add caution about combining excluded_http_codes with passthru_level

Author: OskarStark

logging/monolog_exclude_http_codes.rst

@@ -59,3 +59,10 @@ logging these HTTP codes based on the MonologBundle configuration:
                 ],
             ],
         ]);
+
+.. caution::
+    Combining ``excluded_http_codes`` with a ``passthru_level`` lower than
+    ``error`` (i.e. ``debug``, ``info``, ``notice`` or ``warning``) will not
+    actually exclude log messages for those HTTP codes because they are logged
+    with level of ``error`` or higher and ``passthru_level`` takes precedence
+    over the HTTP codes being listed in ``excluded_http_codes``.