Use unique names for temporary directories in punctuation and capitalization tests

Use `mktemp -d` for creating temporary directories for punctuation and capitalization model tests. Previously race conditions happened if several similar tests were run on same machine.

**Collection**: nlp
  
**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.

