fix: 修复全局变量名称出现特殊字符的问题

--bug=1047017 --user=刘瑞斌 【应用编排】添加全局变量，变量应该限制字符类型，不然引用会报错 https://www.tapd.cn/57709429/s/1584342

ui/src/workflow/nodes/base-node/component/FieldFormDialog.vue

@@ -132,7 +132,7 @@ const form = ref<any>({
 
 const rules = reactive({
   name: [{ required: true, message: '请输入变量名', trigger: 'blur' }],
-  variable: [{ required: true, message: '请输入变量', trigger: 'blur' }],
+  variable: [{ required: true, message: '请输入变量', trigger: 'blur' }, { pattern: /^[a-zA-Z_]+$/, message: '只能输入字母和下划线', trigger: 'blur' } ],
   default_value: [{ required: true, message: '请输入默认值', trigger: 'blur' }]
 })