Timezone parsing accepts invalid values

Issue Description

This is accepted as a valid timezone expression, and should not be: +03:00.34

Note that this is a regression, and this PR would fix it: https://github.com/arrow-py/arrow/pull/1165

System Info

• OS name and version: Ubuntu 25.10
• Python version: Python 3.13.7
• Arrow version: 1.4.0