fix(tests): correct import path for git_helper module in updatenotification tests

[KristjanESPERANTO]

This removes a warning which appeared running a test:

$ npx vitest --run tests/unit/functions/updatenotification_spec.js

 RUN  v4.1.2

7:46:46 PM [vite] (ssr) warning: invalid import "../../../${defaults.defaultModulesDir}/updatenotification/git_helper". A file extension must be included in the static part of the import. For example: import(`./foo/${bar}.js`).

Related to #4073