[charts] Fix key generation for the ChartsGrid (@alexfauquette) (#15864)

Co-authored-by: Alexandre Fauquette <[email protected]>

Author: JCQuintas

Diff for: packages/x-charts/src/ChartsGrid/ChartsHorizontalGrid.tsx

@@ -23,9 +23,9 @@ export function ChartsGridHorizontal(props: ChartsGridHorizontalProps) {
 
   return (
     <React.Fragment>
-      {yTicks.map(({ formattedValue, offset }) => (
+      {yTicks.map(({ value, offset }) => (
         <GridLine
-          key={`horizontal-${formattedValue}`}
+          key={`horizontal-${value}`}
           y1={offset}
           y2={offset}
           x1={drawingArea.left}

Diff for: packages/x-charts/src/ChartsGrid/ChartsVerticalGrid.tsx

@@ -23,9 +23,9 @@ export function ChartsGridVertical(props: ChartsGridVerticalProps) {
 
   return (
     <React.Fragment>
-      {xTicks.map(({ formattedValue, offset }) => (
+      {xTicks.map(({ value, offset }) => (
         <GridLine
-          key={`vertical-${formattedValue}`}
+          key={`vertical-${value}`}
           y1={drawingArea.top}
           y2={drawingArea.top + drawingArea.height}
           x1={offset}