[IMP] error message on wrong file format

[emjay0921]

Why is this change needed?

How was the change implemented?

New unit tests

Unit tests executed by the author

How to test manually

Related links

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.85%. Comparing base (f172ecf) to head (33a112e).

Files with missing lines	Patch %	Lines
spp_area_base/models/area_import.py	40.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             17.0     #845      +/-   ##
==========================================
- Coverage   77.88%   77.85%   -0.04%     
==========================================
  Files         763      763              
  Lines       19853    19857       +4     
  Branches     2383     2384       +1     
==========================================
- Hits        15463    15459       -4     
- Misses       3835     3841       +6     
- Partials      555      557       +2     

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