chore: rename form `accept-charset` attribute (#16478)

* chore: rename form accept-charset attribute

* chore: utf-8 to lowercase

Co-authored-by: Rich Harris <hello@rich-harris.dev>

* Update .changeset/healthy-carpets-deny.md

---------

Co-authored-by: Rich Harris <hello@rich-harris.dev>

.changeset/healthy-carpets-deny.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: rename form accept-charset attribute

packages/svelte/elements.d.ts

@@ -996,7 +996,7 @@ export interface HTMLFieldsetAttributes extends HTMLAttributes<HTMLFieldSetEleme
 }
 
 export interface HTMLFormAttributes extends HTMLAttributes<HTMLFormElement> {
-	acceptcharset?: string | undefined | null;
+	'accept-charset'?: 'utf-8' | (string & {}) | undefined | null;
 	action?: string | undefined | null;
 	autocomplete?: AutoFillBase | undefined | null;
 	enctype?: