Fix typo in Python documentation

Oleg pointed out that when renaming from "status" to "enabled" in the
Python TUI events patch, I neglected to update one spot in the
documentation.  This patch fixes this.  I'm checking it in as obvious.

You can verify that this change is correct by examining
gdb/python/py-event-types.def.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32162