Fix non-strings in sendpoi

[rikroe]

Proposed change

Fixes parsing of POI with numeric postcodes.

Type of change

• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (which adds functionality to this library)
• [ ] Breaking change (fix/feature causing existing functionality to break)
• [ ] Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:

Checklist

• [x] The code change is tested and works locally.
• [x] Tests have been added to verify that the new code works.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (9d3bd67) 100.00% compared to head (3a52e1e) 100.00%. Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #590 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 17 17 Lines 1412 1412 ========================================= Hits 1412 1412 ``` | [Flag](https://app.codecov.io/gh/bimmerconnected/bimmer_connected/pull/590/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bimmerconnected) | Coverage Δ | | |---|---|---| | [3.10](https://app.codecov.io/gh/bimmerconnected/bimmer_connected/pull/590/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bimmerconnected) | `100.00% <100.00%> (ø)` | | | [3.11](https://app.codecov.io/gh/bimmerconnected/bimmer_connected/pull/590/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bimmerconnected) | `100.00% <100.00%> (ø)` | | | [3.12](https://app.codecov.io/gh/bimmerconnected/bimmer_connected/pull/590/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bimmerconnected) | `100.00% <100.00%> (ø)` | | | [3.8](https://app.codecov.io/gh/bimmerconnected/bimmer_connected/pull/590/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bimmerconnected) | `100.00% <100.00%> (ø)` | | | [3.9](https://app.codecov.io/gh/bimmerconnected/bimmer_connected/pull/590/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bimmerconnected) | `100.00% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bimmerconnected#carryforward-flags-in-the-pull-request-comment) to find out more.

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