Use separate variable for array and set of legend values

This is easier for the compiler to understand.

src/util/colorScale.ts

@@ -418,7 +418,7 @@ export function createVisibleLegendValues({
     // filter according to scaleType, e.g. continuous is different to categorical which is different to boolean
     // filtering will involve looping over reduxState.tree.nodes and comparing with reduxState.tree.visibility
     if (scaleType === "ordinal" || scaleType === "categorical") {
-      let legendValuesObserved: string[] | Set<string> = treeNodes
+      let legendValuesObserved: string[] = treeNodes
         .filter((n, i) => (!n.hasChildren && visibility[i]===NODE_VISIBLE))
         .map((n) => genotype ? n.currentGt : getTraitFromNode(n, colorBy));
       // if the 2nd tree is enabled, compute visible legend values and merge the values.
@@ -428,8 +428,8 @@ export function createVisibleLegendValues({
           .map((n) => genotype ? n.currentGt : getTraitFromNode(n, colorBy));
         legendValuesObserved = [...legendValuesObserved, ...legendValuesObservedToo];
       }
-      legendValuesObserved = new Set(legendValuesObserved);
-      const visibleLegendValues = legendValues.filter((v) => legendValuesObserved.has(v));
+      const legendValuesObservedSet = new Set(legendValuesObserved);
+      const visibleLegendValues = legendValues.filter((v) => legendValuesObservedSet.has(v));
       return visibleLegendValues;
     }
   }