Fix flaky tests in ParserTest.java (#15318)

Fixed the following flaky tests:

    org.apache.druid.math.expr.ParserTest#testApplyFunctions
    org.apache.druid.math.expr.ParserTest#testSimpleMultiplicativeOp1
    org.apache.druid.math.expr.ParserTest#testFunctions
    org.apache.druid.math.expr.ParserTest#testSimpleLogicalOps1
    org.apache.druid.math.expr.ParserTest#testSimpleAdditivityOp1
    org.apache.druid.math.expr.ParserTest#testSimpleAdditivityOp2

The above mentioned tests have been reported as flaky (tests assuming deterministic implementation of a non-deterministic specification ) when ran against the NonDex tool.
The tests contain assertions (Assertion 1 & Assertion 2) that compare an ArrayList created from a HashSet using the ArrayList() constructor with another List. However, HashSet does not guarantee the ordering of elements and thus resulting in these flaky tests that assume deterministic implementation of HashSet. Thus, when the NonDex tool shuffles the HashSet elements, it results in the test failures:

Co-authored-by: ythorat2 <ythorat2@illinois.edu>

processing/src/test/java/org/apache/druid/math/expr/ParserTest.java

@@ -38,6 +38,7 @@ import org.junit.rules.ExpectedException;
 import java.math.BigInteger;
 import java.nio.ByteBuffer;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -820,7 +821,7 @@ public class ParserTest extends InitializedNullHandlingTest
     }
     final Expr.BindingAnalysis deets = parsed.analyzeInputs();
     Assert.assertEquals(expression, expected, parsed.toString());
-    Assert.assertEquals(expression, identifiers, deets.getRequiredBindingsList());
+    Assert.assertEquals(expression, new HashSet<>(identifiers), deets.getRequiredBindings());
     Assert.assertEquals(expression, scalars, deets.getScalarVariables());
     Assert.assertEquals(expression, arrays, deets.getArrayVariables());
 
@@ -828,7 +829,7 @@ public class ParserTest extends InitializedNullHandlingTest
     final Expr roundTrip = Parser.parse(parsedNoFlatten.stringify(), ExprMacroTable.nil());
     Assert.assertEquals(parsed.stringify(), roundTrip.stringify());
     final Expr.BindingAnalysis roundTripDeets = roundTrip.analyzeInputs();
-    Assert.assertEquals(expression, identifiers, roundTripDeets.getRequiredBindingsList());
+    Assert.assertEquals(expression, new HashSet<>(identifiers), roundTripDeets.getRequiredBindings());
     Assert.assertEquals(expression, scalars, roundTripDeets.getScalarVariables());
     Assert.assertEquals(expression, arrays, roundTripDeets.getArrayVariables());
   }