Fix strict error handling in developer tools templates (#12352)

src/data/ws-templates.ts

@@ -20,6 +20,7 @@ export const subscribeRenderTemplate = (
     entity_ids?: string | string[];
     variables?: Record<string, unknown>;
     timeout?: number;
+    strict?: boolean;
   }
 ): Promise<UnsubscribeFunc> =>
   conn.subscribeMessage((msg: RenderTemplateResult) => onChange(msg), {

src/panels/developer-tools/template/developer-tools-template.ts

@@ -329,6 +329,7 @@ class HaPanelDevTemplate extends LitElement {
         {
           template: this._template,
           timeout: 3,
+          strict: true,
         }
       );
       await this._unsubRenderTemplate;