CI failures that appear to be related to the length of the file name

[mununki]

https://github.com/rescript-lang/rescript-compiler/pull/6414

Regarding the above PR, it appears that the cause of the CI test (ciTest.js) failing is related to the fixture filename. For example, for a file name like curried_value_instead_of uncurried_in_curried_mode.res, the test failed on all platforms. For c_value_wanted_u_in_c_mode.res, it only failed on mac. For c_for_u_in_c_mode, the test passed on all platforms.

We have fixture files with longer names than this in the past, so we suspect that the issue is with the use of characters like _ rather than simply the length of the file name.