[Go SDK] Replace deprecated reflect.PtrTo in schema test

[Eliaaazzz]

Follow-up to #40153. @Abacn pointed out in #40153 (comment) that reflect.PtrTo has been deprecated since Go 1.22. The test added there now calls reflect.PointerTo, and the two functions behave identically.

Part of #39684.

[Abacn]

Thanks!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 28.62%. Comparing base (76f6e6d) to head (1effd7b).
⚠️ Report is 141 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #40544       +/-   ##
=============================================
- Coverage     56.16%   28.62%   -27.55%     
=============================================
  Files          1124      380      -744     
  Lines        178336    70974   -107362     
  Branches       1489        0     -1489     
=============================================
- Hits         100170    20316    -79854     
+ Misses        75645    48819    -26826     
+ Partials       2521     1839      -682     

Flag	Coverage Δ
go	28.62% <ø> (-0.52%)	⬇️
java	?
python	?

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R: @shunping for label go.

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