Fix gpu regression tests
This MR fixes some issues that were present with MLIR builds using GPU (the issues were discovered through regression test failures).
When running regression tests, there are still some validation failures for ionic models (AslanidiSleiman, Bondarenko, Shannon and tenTusscherPanfilov) because of precision issues (a maximum error of 7e-4 for the Bondarenko model compared to the reference, the tolerence being set to 1e-6 by default). We suspect that those issues come from the implementation on math functions like exp, or sin / cos which is different on GPU. If I remember correctly, @axel.loewe mentioned that the error was acceptable.