fix(tests): generator tests on linux

[rachel-fenichel]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide
• I ran npm run format and npm run lint

The details

Resolves

Fixes an issue where the generator tests fail on Linux with

fenichel@fenichel-glaptop2:~/Documents/gblockly-rr$ npm run test:generators

> [email protected] test:generators
> gulp --silent testGenerators

=======================================
== generators
Cannot read properties of null (reading 'code')
FAILED: generators
fenichel@fenichel-glaptop2:~/Documents/gblockly-rr$

Proposed Changes

Remove trailing slashes from calls to rimraf.

Behavior Before Change

Crashes on linux

Behavior After Change

Tests run and don't crash.

Reason for Changes

Rimraf didn't like the trailing slash, which is surprising to me.

Additional Information

Caused by #6431 so we'll need to verify it still works on windows after this fix.