Allow schools without address in schema

[k-nut]

The Grundschule Abtsdorf "Ferdinand Freiligrath" (ST-ARC00839) and ~800 more schools from Sachsen-Anhalt don't have an address field stored in the database. Our parser refuses to load them. We cannot control this though so we'll adapt the schema instead.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.56%. Comparing base (9b558c3) to head (30c66d3).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #28   +/-   ##
=======================================
  Coverage   96.56%   96.56%           
=======================================
  Files           8        8           
  Lines         407      407           
=======================================
  Hits          393      393           
  Misses         14       14           

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