Frontmatter containing $1 is correctly substituted

Without this change, the script itself would be inserted into the metadata string

Before:
```svelte
<script·context="module">
export const metadata = {"price":"<script·context="module">0"};
const {·price·} = metadata;
</script>
```

After:
<script context="module">
export const metadata = {"price":"$10"};
const { price } = metadata;
</script>

packages/mdsvex/src/transformers/index.ts

@@ -380,7 +380,7 @@ export function transform_hast({
 				// @ts-ignore
 				_module[0].value = _module[0].value.replace(
 					RE_MODULE_SCRIPT,
-					`$1${newline}\t${fm}`
+					(match: string) => `${match}${newline}\t${fm}`
 				);
 			}
 

packages/mdsvex/test/_fixtures/hybrid/input/dollar-one-in-frontmatter.svx

@@ -0,0 +1,5 @@
+---
+price: '$10'
+---
+<script context="module">
+</script>

packages/mdsvex/test/_fixtures/hybrid/output/dollar-one-in-frontmatter.svelte

@@ -0,0 +1,4 @@
+<script context="module">
+export const metadata = {"price":"$10"};
+const { price } = metadata;
+</script>