doc: fix typo in writing-test.md

Corrects the misspelling of "optimial" to "optimal".

PR-URL: https://github.com/nodejs/node/pull/59123
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ulises Gascón <ulisesgascongonzalez@gmail.com>

doc/contributing/writing-tests.md

@@ -24,7 +24,7 @@ See [directory structure overview][] for outline of existing test and locations.
 
 ## How to write a good test
 
-A good test should be written in a style that is optimial for debugging
+A good test should be written in a style that is optimal for debugging
 when it fails.
 
 In principle, when adding a new test, it should be placed in a new file.