chore: fix test_subslice_offset.
chore: fix test_subslice_offset.

*If* the compiler *happened* to put the two test strings next to each
other in the binary, this would fail.  Whoopsie!

And yes, the implementation stays as-is: changing it breaks other stuff.

DanielKeep/rust-scan-rules,DanielKeep/rust-scan-rules