fix: Avoid duplicated requestable fields (sourcenetwork#1621)

## Relevant issue(s)

Resolves sourcenetwork#1615

## Description

Makes sure the requestable fields aren't duplicated

planner/mapper/mapper.go

@@ -795,6 +795,7 @@ func resolveInnerFilterDependencies(
 ) ([]Requestable, error) {
 	newFields := []Requestable{}
 
+sourceLoop:
 	for key := range source {
 		if strings.HasPrefix(key, "_") && key != request.KeyFieldName {
 			continue
@@ -844,6 +845,11 @@ func resolveInnerFilterDependencies(
 			// If the key index is outside the bounds of the child mapping array, then
 			// this is not a relation/join and we can add it to the fields and
 			// continue (no child props to process)
+			for _, field := range existingFields {
+				if field.GetIndex() == keyIndex {
+					continue sourceLoop
+				}
+			}
 			newFields = append(existingFields, &Field{
 				Index: keyIndex,
 				Name:  key,