Fix not registering object types when interface type is used as object type field type

[MichalLytek]

Closes #726 🔒

[codecov]

Codecov Report

Merging #736 into master will decrease coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #736      +/-   ##
==========================================
- Coverage   95.40%   95.33%   -0.07%     
==========================================
  Files          80       80              
  Lines        1479     1480       +1     
  Branches      294      294              
==========================================
  Hits         1411     1411              
- Misses         65       66       +1     
  Partials        3        3              

Impacted Files	Coverage Δ
src/schema/schema-generator.ts	97.68% <100.00%> (-0.33%)	⬇️

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