If you received this patch from someone you trusted, and noticed the period, would you call it a typo or would you assume it is malicious?

Or is this just an argument over the use of the word "typo" instead of "mistake"? That wouldn't be very useful, IMO.

Very common if you copy paste (using mouse buffer) from midnight commander text editor or any other editor that highlights trailing spaces as dot.

I take it they're not forcing contributors to lint code, then?

Does your linter look for syntax errors in the content of strings? If so, how would you design a unit test meant to capture syntax errors?

Have you tried running lint on a configure.ac or CMakeLists.txt file?

For those using editors with mouse, it's very easy to add a character anywhere. Doesn't matter the place.