fix: note old eslint plugin deprecation (#10319)

closes #10242

Author: dummdidumm

.changeset/two-terms-remain.md

@@ -0,0 +1,5 @@
+---
+'svelte-migrate': patch
+---
+
+fix: note old eslint plugin deprecation

packages/migrate/migrations/svelte-4/migrate.js

@@ -44,6 +44,11 @@ export function update_pkg_json_content(content) {
 	update_pkg('rollup-plugin-svelte', '^7.1.5');
 	update_pkg('prettier-plugin-svelte', '^2.10.1');
 	update_pkg('eslint-plugin-svelte', '^2.30.0');
+	update_pkg(
+		'eslint-plugin-svelte3',
+		'^4.0.0',
+		' (this package is deprecated, use eslint-plugin-svelte instead. More info: https://svelte.dev/docs/v4-migration-guide#new-eslint-package)'
+	);
 	update_pkg(
 		'typescript',
 		'^5.0.0',