ci.kaitai.io: use snake_case for test names instead of PascalCase
The original KSY specifications is written in snake_case, but in the test matrix at https://ci.kaitai.io/ test names converted to PascalCase. It makes quite difficult to find a source KSY to check the test.

Even better, if test name would by hyperlink to the file in [github repository](https://github.com/kaitai-io/kaitai_struct_tests/tree/master/formats) at time of matrix building.