errors: make use of "cannot" consistent
We frequently use the word "cannot" in error messages, this is the only occurrence of "can not". I am not a native English speaker, but according to various resources, the former should generally be preferred over the latter, and is probably what native speakers would expect.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines