Fix fuzz different output types for generated expression sets in expr…

…ession fuzzer (#7910)

Summary:
Pull Request resolved: #7910

A previous refactor resulted in a bug that makes all the fields of the fuzzed expression
final output be of the same type.

This fix it.

Reviewed By: kagamiori

Differential Revision: D51926820

fbshipit-source-id: 4b1fc0e035d9d1887ad1a2dc7183849bcc3783c4

velox/expression/tests/ExpressionFuzzer.cpp

@@ -1009,10 +1009,9 @@ ExpressionFuzzer::FuzzedExpressionData ExpressionFuzzer::fuzzExpressions(
   VELOX_CHECK_EQ(
       state.remainingLevelOfNesting_, std::max(1, options_.maxLevelOfNesting));
 
-  auto outType = fuzzReturnType();
-
   std::vector<core::TypedExprPtr> expressions;
   for (int i = 0; i < numberOfExpressions; i++) {
+    auto outType = fuzzReturnType();
     expressions.push_back(generateExpression(outType));
   }
   return {