Fix the size of the tab not being fixed after being justified on "fully"

[oppZ]

Type of changes

• [x] Bug fix
• [ ] New feature
• [ ] Documentation / docstrings
• [ ] Tests
• [ ] Other

Checklist

• [x] I've run the latest black with default args on new code.
• [x] I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• [ ] I've added tests for new code.
• [x] I accept that @willmcgugan may be pedantic in the code review.

Description

Fixes : https://github.com/Textualize/rich/issues/3424

Before :

After :