fix(compiler-core): improve reg for v-on function expression

Author: hchlq

packages/compiler-core/src/transforms/vOn.ts

@@ -17,7 +17,7 @@ import { hasScopeRef, isMemberExpression } from '../utils'
 import { TO_HANDLER_KEY } from '../runtimeHelpers'
 
 const fnExpRE =
-  /^\s*([\w$_]+|(async\s*)?(\([^)]*?\)|[^=]+))\s*=>|^\s*(async\s+)?function(?:\s+[\w$]+)?\s*\(/
+  /^\s*(async\s*)?(\([^)]*?\)|[\w$_]+)\s*=>|^\s*(async\s+)?function(?:\s+[\w$]+)?\s*\(/
 
 export interface VOnDirectiveNode extends DirectiveNode {
   // v-on without arg is handled directly in ./transformElements.ts due to it affecting