Fix failed assertion for assignment in expression context

This code path is reachable for all assignments expressions, not just true
variable expressions.

Really surprising we have no tests that caught this.

Zend/tests/gh20628_005.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Failed assertion for assignment in expression context
+--CREDITS--
+Matteo Beccati (mbeccati)
+--FILE--
+<?php
+
+function foo() {
+    return ['bar' => 'baz'];
+}
+
+var_dump(($v = foo())['bar'], $v);
+
+?>
+--EXPECT--
+string(3) "baz"
+array(1) {
+  ["bar"]=>
+  string(3) "baz"
+}

Zend/zend_compile.c

@@ -12303,7 +12303,6 @@ static zend_op *zend_compile_var_inner(znode *result, zend_ast *ast, uint32_t ty
 			zend_compile_assign_ref(result, ast, type);
 			return NULL;
 		case ZEND_AST_ASSIGN:
-			ZEND_ASSERT(ast->child[0]->kind == ZEND_AST_ARRAY && zend_propagate_list_refs(ast->child[0]));
 			zend_compile_assign(result, ast, false, type);
 			return NULL;
 		default: