tools: remove bashisms from license builder script
In preparation for https://github.com/nodejs/node/pull/36099
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
In preparation for https://github.com/nodejs/node/pull/36099
make -j4 test
(UNIX), or vcbuild test
(Windows) passes