[Interactive Graph] Update the axis labels to be TeX by default again (#3028)

## Summary:
It looks like these are defaulting to `x` and `y` instead of `$x$` and `$y$`.

Changing them to be `$x$` and `$y$` as requested by content authors.

Issue: none

Test plan:
`pnpm jest packages/perseus/src/widgets/interactive-graphs/serialize-interactive-graph.test.ts`

Storybook
- Go to `/?path=/story/editors-editorpage--demo`
- Add a new interactive graph
- Scroll to the common settings
- Confirm that the axis labels are `$x$` and `$y$`

| Before | After |
| --- | --- |
| <img width="376" height="283" alt="Screenshot 2025-11-12 at 11 45 40 AM" src="https://github.com/user-attachments/assets/5b194b25-5857-4a80-ba85-026f52b6ccb6" /> | <img width="377" height="278" alt="Screenshot 2025-11-12 at 11 45 44 AM" src="https://github.com/user-attachments/assets/dfe844cc-3e10-46b0-98b1-61141d9a4189" /> |

Author: nishasy

Reviewers: mark-fitzgerald

Required Reviewers:

Approved By: mark-fitzgerald

Checks: ⏹️  7 checks were cancelled, ✅ 3 checks were successful

Pull Request URL: #3028

Author: nishasy

.changeset/twenty-turkeys-lay.md

@@ -0,0 +1,6 @@
+---
+"@khanacademy/perseus": patch
+"@khanacademy/perseus-core": patch
+---
+
+[Interactive Graph] Update the axis labels to be TeX by default again

packages/perseus-core/src/parse-perseus-json/regression-tests/__snapshots__/parse-perseus-json-regression.test.ts.snap

@@ -9733,8 +9733,8 @@ exports[`parseAndMigratePerseusItem given interactive-graph-missing-labels.ts re
           },
           "labelLocation": "onAxis",
           "labels": [
-            "x",
-            "y",
+            "$x$",
+            "$y$",
           ],
           "lockedFigures": [],
           "markings": "none",

packages/perseus-core/src/widgets/interactive-graph/index.ts

@@ -23,7 +23,7 @@ export type InteractiveGraphDefaultWidgetOptions = Pick<
 >;
 
 const defaultWidgetOptions: InteractiveGraphDefaultWidgetOptions = {
-    labels: ["x", "y"],
+    labels: ["$x$", "$y$"],
     labelLocation: "onAxis",
     range: [
         [-10, 10],

packages/perseus/src/widgets/interactive-graphs/interactive-graph.tsx

@@ -265,7 +265,7 @@ class InteractiveGraph extends React.Component<Props, State> {
     mafsRef = React.createRef<StatefulMafsGraphType>();
 
     static defaultProps: DefaultProps = {
-        labels: ["x", "y"],
+        labels: ["$x$", "$y$"],
         labelLocation: "onAxis",
         range: [
             [-10, 10],

packages/perseus/src/widgets/interactive-graphs/serialize-interactive-graph.test.ts

@@ -117,7 +117,7 @@ describe("InteractiveGraph serialization", () => {
                 "interactive-graph 1": {
                     alignment: "default",
                     static: false,
-                    labels: ["x", "y"],
+                    labels: ["$x$", "$y$"],
                     labelLocation: "onAxis",
                     range: [
                         [-10, 10],