fix: new alert should have force_screenshot be true (apache#18182)

* fix: new alert should have force_screenshot be true

* fix comments

superset-frontend/src/views/CRUD/alert/AlertReportModal.tsx

@@ -516,10 +516,11 @@ const AlertReportModal: FunctionComponent<AlertReportModalProps> = ({
       }
     });
 
+    const shouldEnableForceScreenshot = contentType === 'chart' && !isReport;
     const data: any = {
       ...currentAlert,
       type: isReport ? 'Report' : 'Alert',
-      force_screenshot: forceScreenshot ? 'true' : 'false',
+      force_screenshot: shouldEnableForceScreenshot || forceScreenshot,
       validator_type: conditionNotNull ? 'not null' : 'operator',
       validator_config_json: conditionNotNull
         ? {}
@@ -862,6 +863,8 @@ const AlertReportModal: FunctionComponent<AlertReportModalProps> = ({
 
   const onContentTypeChange = (event: any) => {
     const { target } = event;
+    // When switch content type, reset force_screenshot to false
+    setForceScreenshot(false);
     // Gives time to close the select before changing the type
     setTimeout(() => setContentType(target.value), 200);
   };