Reduce precision of oklab() arguments in test snapshots

[philipp-spiess]

After the changes in #15201, our Windows CI started to fail. The problem is that lightningcss now needs to convert oklch colors into the oklab space to inline some color-mix() functions.

The problem, though, is that this calculation seems to have rounding differences between macOS, Linux, and Windows. Since we still want to define the default color space in oklch and use lightningcss as a post-processor in our unit tests so we have a better coverage of the output, this PR attempts to fix the issue by adding a custom vitest serializer. It will find usages of the oklab() function with arguments that have lots of decimal places (at least 6 decimal places). What it then does is simply cut off any excess decimal places to truncate the output to 5 places. E.g.:

- oklab(62.7955% .224863 .125846 / .75);
+ oklab(62.7955% .22486 .12584 / .75);

Test Plan

I updated the CI workflow file to make all three builds run in CI and observed that they are now all green again.