chore: add test cases for oneOf support

[n1ru4l]

Backport of graphql/graphql-js@29144f7

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Latest commit: 3a6a389

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[github-actions]

✅ Benchmark Results

     ✓ no_errors
     ✓ expected_result

     checks.........................: 100.00% ✓ 326       ✗ 0  
     data_received..................: 38 MB   3.8 MB/s
     data_sent......................: 140 kB  14 kB/s
     http_req_blocked...............: avg=3.93µs   min=2.22µs   med=2.76µs   max=157.78µs p(90)=3.88µs   p(95)=4.25µs  
     http_req_connecting............: avg=631ns    min=0s       med=0s       max=102.96µs p(90)=0s       p(95)=0s      
     http_req_duration..............: avg=57.27ms  min=49.06ms  med=53.67ms  max=151.87ms p(90)=63.81ms  p(95)=86.7ms  
       { expected_response:true }...: avg=57.27ms  min=49.06ms  med=53.67ms  max=151.87ms p(90)=63.81ms  p(95)=86.7ms  
     http_req_failed................: 0.00%   ✓ 0         ✗ 163
     http_req_receiving.............: avg=144.16µs min=115.45µs med=133.99µs max=865.89µs p(90)=161.35µs p(95)=185.43µs
     http_req_sending...............: avg=24.68µs  min=18.25µs  med=22.98µs  max=59.45µs  p(90)=29.19µs  p(95)=32.61µs 
     http_req_tls_handshaking.......: avg=0s       min=0s       med=0s       max=0s       p(90)=0s       p(95)=0s      
     http_req_waiting...............: avg=57.1ms   min=48.9ms   med=53.5ms   max=151.44ms p(90)=63.66ms  p(95)=86.5ms  
     http_reqs......................: 163     16.230329/s
     iteration_duration.............: avg=61.59ms  min=52.66ms  med=57.83ms  max=155.84ms p(90)=73.83ms  p(95)=91.31ms 
     iterations.....................: 163     16.230329/s
     vus............................: 1       min=1       max=1
     vus_max........................: 1       min=1       max=1

[github-actions]

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