Fix: lv_LV postcode format

[edgarsn]

What is the reason for this PR?

This fixes lv_LV Address provider postcode format to correct one:

• [ ] A new feature
• [x] Fixed an issue (resolve #652 )

Author's checklist

• [x] Follow the Contribution Guide
• [x] New features and changes are documented

Summary of changes

ISO3166-1 alpha-2 country code in front which is LV, next symbol must be dash - and then 4 digits. e.g. LV-1000, instead of LV 1000

https://en.wikipedia.org/wiki/Postal_codes_in_Latvia

Review checklist

• [ ] All checks have passed
• [ ] Changes are approved by maintainer

[bram-pkg]

Thanks for your contribution :)

Could you also update/create a tests?

[edgarsn]

Thanks for your contribution :)

Could you also update/create a tests?

Sorry about that! Test added.

[bram-pkg]

Thank you @edgarsn :)