fix interface for attributeGroup

[beppemarazzi]

Starting from v2.0.711 Interfaces are not more implemented in generated code

[codecov]

Codecov Report

Merging #341 (0e11080) into master (ff78909) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #341      +/-   ##
==========================================
- Coverage   95.51%   95.48%   -0.04%     
==========================================
  Files          20       20              
  Lines        2900     2900              
  Branches      450      450              
==========================================
- Hits         2770     2769       -1     
  Misses         74       74              
- Partials       56       57       +1     

Impacted Files	Coverage Δ
XmlSchemaClassGenerator/ModelBuilder.cs	98.07% <100.00%> (ø)
XmlSchemaClassGenerator/TypeModel.cs	96.43% <0.00%> (-0.10%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ff78909...0e11080. Read the comment docs.

[mganss]

Thanks for catching this regression!

[beppemarazzi]

Thanks for catching this regression!

Thank you for the project!!!!!